Two-dimensional zero padding in a stream of matrix elements

ABSTRACT

Software instructions are executed on a processor within a computer system to configure a steaming engine with stream parameters to define a multidimensional array. The stream parameters define a size for each dimension of the multidimensional array and a specified width for two selected dimensions of the array. Data is fetched from a memory coupled to the streaming engine responsive to the stream parameters. A stream of vectors is formed for the multidimensional array responsive to the stream parameters from the data fetched from memory. When either selected dimension in the stream of vectors exceeds a respective specified width, the streaming engine inserts null elements into each portion of a respective vector for the selected dimension that exceeds the specified width in the stream of vectors. Stream vectors that are completely null are formed by the streaming engine without accessing the system memory for respective data.

TECHNICAL FIELD

This relates to using a streaming engine to insert null elements into astream of matrix elements.

BACKGROUND

Digital signal processors (DSP) are optimized for processing streams ofdata that may be derived from various input signals, such as sensordata, a video stream, a voice channel, radar signals, biomedicalsignals, etc. Digital signal processors operating on real-time datatypically receive an input data stream, perform a filter function on thedata stream (such as encoding or decoding) and output a transformed datastream. The system is called real-time because the application fails ifthe transformed data stream is not available for output when scheduled.Typical video encoding requires a predictable but non-sequential inputdata pattern. A typical application requires memory access to load dataregisters in a data register file and then supply data from the dataregisters to functional units which perform the data processing.

One or more DSP processing cores can be combined with various peripheralcircuits, blocks of memory, etc. on a single integrated circuit (IC) dieto form a system on chip (SoC). These systems can include multipleinterconnected processors that share the use of on-chip and off-chipmemory. A processor can include some combination of instruction cache(ICache) and data cache (DCache) to improve processing. Furthermore,multiple processors with shared memory can be incorporated in a singleembedded system. The processors can physically share the same memorywithout accessing data or executing code located in the same memorylocations or can use some portion of the shared memory as common sharedmemory.

SUMMARY

Methods and apparatus are provided for software instructions to beexecuted on a processor within a computer system to configure a steamingengine with stream parameters to define a multidimensional array. Thestream parameters define a size for each dimension of themultidimensional array and a specified width for two selected dimensionsof the array. Data is fetched from a memory coupled to the streamingengine responsive to the stream parameters. A stream of vectors isformed for the multidimensional array responsive to the streamparameters from the data fetched from memory. When the selecteddimension in the stream of vectors exceeds the specified width, thestreaming inserts null elements into each portion of a respective vectorfor the selected dimension that exceeds the specified width in thestream of vectors. Null elements are inserted into respective vectorsfor each of the two selected dimensions. Stream vectors that arecompletely null are formed by the streaming engine without accessing thesystem memory for respective data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example dual scalar/vector data path processor.

FIG. 2 illustrates the registers and functional units in the dualscalar/vector data path processor illustrated in FIG. 1.

FIG. 3 illustrates a global scalar register file.

FIG. 4 illustrates a local scalar register file shared by arithmeticfunctional units.

FIG. 5 illustrates a local scalar register file shared by multiplyfunctional units.

FIG. 6 illustrates a local scalar register file shared by load/storeunits.

FIG. 7 illustrates a global vector register file.

FIG. 8 illustrates a predicate register file.

FIG. 9 illustrates a local vector register file shared by arithmeticfunctional units.

FIG. 10 illustrates a local vector register file shared by multiply andcorrelation functional units.

FIG. 11 illustrates pipeline phases of a processing unit.

FIG. 12 illustrates sixteen instructions of a single fetch packet.

FIG. 13 illustrates an example of the instruction coding ofinstructions.

FIG. 14 illustrates bit coding of a condition code extension slot 0.

FIG. 15 illustrates bit coding of a condition code extension slot 1.

FIG. 16 illustrates bit coding of a constant extension slot 0.

FIG. 17 is a partial block diagram illustrating constant extension.

FIG. 18 illustrates carry control for SIMD operations.

FIG. 19 illustrates a conceptual view of streaming engines.

FIG. 20 illustrates a sequence of formatting operations.

FIG. 21 illustrates an example of lane allocation in a vector.

FIG. 22 illustrates an example of lane allocation in a vector.

FIG. 23 illustrates a basic two-dimensional (2D) stream.

FIG. 24 illustrates the order of elements within the example stream ofFIG. 23.

FIG. 25 illustrates extracting a smaller rectangle from a largerrectangle.

FIG. 26 illustrates how an example streaming engine fetches a streamwith a transposition granularity of 4 bytes.

FIG. 27 illustrates how an example streaming engine fetches a streamwith a transposition granularity of 8 bytes.

FIG. 28 illustrates the details of an example streaming engine.

FIG. 29 illustrates an example stream template register.

FIG. 30 illustrates sub-field definitions of the flags field of theexample stream template register of FIG. 29.

FIG. 31 illustrates an example of a vector length masking/groupduplication block.

FIG. 32 is a partial schematic diagram of an example of the generationof the streaming engine valid or invalid indication.

FIG. 33 is a partial schematic diagram of a streaming engine addressgenerator illustrating generation of the loop address and loop count.

FIG. 34 illustrates a partial schematic diagram showing the streamingengine supply of data of this example.

FIG. 35 illustrates a partial schematic diagram showing the streamingengine supply of valid data to the predicate unit.

FIG. 36 is a block diagram of a system that includes a matrixmultiplication accelerator and the streaming engine of FIG. 28.

FIG. 37 illustrates an example of matrix multiplication.

FIG. 38 is a more detailed block diagram of a portion of the streamingengine of FIG. 28.

FIGS. 39, 40, 41, 42, and 43 illustrate example linear stream transfersby the streaming engine of FIG. 28.

FIGS. 44A, 44B together illustrate how a partial matrix is augmentedwith null vectors by the streaming engine of FIG. 28 for matrixmultiplication.

FIG. 45 illustrates adding null vectors to a stream.

FIGS. 46-47 illustrate formation of a stream by inserting null orpredefined data vectors by the streaming engine of FIG. 28.

FIG. 48 is a block diagram of a multiprocessor system that includes thestreaming engine of FIG. 28.

DETAILED DESCRIPTION

In the drawings, like elements are denoted by like reference numeralsfor consistency.

Digital signal processors (DSP) are optimized for processing streams ofdata that may be derived from various input signals, such as sensordata, a video stream, a voice channel, radar signals, biomedicalsignals, etc. Memory bandwidth and scheduling are concerns for digitalsignal processors operating on real-time data. An example DSP isdescribed herein that includes a streaming engine to improve memorybandwidth and data scheduling.

One or more DSP can be combined with various peripheral circuits, blocksof memory, etc. on a single integrated circuit (IC) die to form a systemon chip (SoC). See, for example, “66AK2Hx Multicore Keystone™ DSP+ARM®System-on-Chip,” 2013 which is incorporated by reference herein.

In the example processor described herein, an autonomous streamingengine (SE) is coupled to the DSP. In this example, the streaming engineincludes two closely coupled streaming engines that can manage two datastreams simultaneously. In another example, the streaming engine iscapable of managing only a single stream, while in other examples thestreaming engine is capable of handling more than two streams. In eachcase, for each stream, the streaming engine includes an addressgeneration stage, a data formatting stage, and some storage forformatted data waiting for consumption by the processor. In the examplesdescribed herein, addresses are derived from algorithms that can involvemulti-dimensional loops, each dimension maintaining an iteration count.In one example, the streaming engine supports six levels of nestediteration. In other examples, more or fewer levels of iteration aresupported.

In the example processor described hereinbelow, control logic and analignment network enable the streaming engine to form null vectors orpadded vectors and to insert them into two dimensions of a streamwithout accessing the null data or pad data from system memory.

Several examples of forming null vectors and padded vectors aredescribed in more detail with regards to FIGS. 36-48.

An example DSP processor is described in detail herein with reference toFIGS. 1-18. An example streaming engine capable of managing two datastreams using six-dimensional nested loops is described in detail hereinwith reference to FIGS. 19-35.

FIG. 1 illustrates an example processor 100 that includes dualscalar/vector data paths 115, 117. As used herein, the term “vector”refers to a one-dimensional array of data elements that can be accessedand operated on as a unit. Processor 100 includes a streaming engine 125that is described in more detail herein. Processor 100 includes separatelevel one instruction cache (L1I) 121 and level one data cache (L1D)123. Processor 100 includes a level 2 (L2) combined instruction/datacache 130 that holds both instructions and data. FIG. 1 illustratesconnection between L1I cache and L2 combined instruction/data cache 130,512-bit bus 142. FIG. 1 illustrates the connection between L1D cache 123and L2 combined instruction/data cache 130, 512-bit bus 145. In theexample processor 100, L2 combined instruction/data cache 130 storesboth instructions to back up L1I cache 121 and data to back up L1D cache123. In this example, L2 combined instruction/data cache 130 is furtherconnected to higher level cache and/or main memory using known or laterdeveloped memory system techniques not illustrated in FIG. 1. As usedherein, the term “higher level” memory or cache refers to a next levelin a memory hierarchy that is more distant from the processor, while theterm “lower level” memory or cache refers to a level in the memoryhierarchy that is closer to the processor. L1I cache 121, L1D cache 123,and L2 cache 130 may be implemented in different sizes in variousexamples. In this example, L1I cache 121 and L1D cache 123 are each 32Kbytes, and L2 cache 130 is 1024K bytes. In the example processor 100,L1I cache 121, L1D cache 123 and L2 combined instruction/data cache 130are formed on a single integrated circuit. This single integratedcircuit optionally includes other circuits.

Processing unit core 110 fetches instructions from L1I cache 121 ascontrolled by instruction fetch unit 111. Instruction fetch unit 111determines the next instructions to be executed and recalls a fetchpacket sized set of such instructions. The nature and size of fetchpackets are further detailed below. Instructions are directly fetchedfrom L1I cache 121 upon a cache hit if the instructions are stored inL1I cache 121. Upon a cache miss occurring when the specifiedinstructions are not stored in L1I cache 121, the instructions aresought in L2 combined cache 130. In this example, the size of a cacheline in L1I cache 121 equals the size of a fetch packet which is 512bits. The memory locations of these instructions are either a hit in L2combined cache 130 or a miss. A hit is serviced from L2 combined cache130. A miss is serviced from a higher level of cache (not illustrated)or from main memory (not illustrated). In this example, the requestedinstruction is simultaneously supplied to both L1I cache 121 andprocessing unit core 110 to speed use.

In this example, processing unit core 110 includes multiple functionalunits to perform instruction specified data processing tasks.Instruction dispatch unit 112 determines the target functional unit ofeach fetched instruction. In this example, processing unit 110 operatesas a very long instruction word (VLIW) processor capable of operating onmultiple instructions in corresponding functional units simultaneously.A complier organizes instructions in execute packets that are executedtogether. Instruction dispatch unit 112 directs each instruction to itstarget functional unit. The functional unit assigned to an instructionis completely specified by the instruction produced by the compiler. Thehardware of processing unit core 110 has no part in the functional unitassignment. In this example, instruction dispatch unit 112 operates onseveral instructions in parallel. The number of such parallelinstructions is set by the size of the execute packet. This is furtherdescribed herein.

One part of the dispatch task of instruction dispatch unit 112 isdetermining whether the instruction is to execute on a functional unitin scalar data path side A 115 or vector data path side B 116. Aninstruction bit within each instruction called the s bit determineswhich data path the instruction controls. This is further describedherein.

Instruction decode unit 113 decodes each instruction in a currentexecute packet. Decoding includes identification of the functional unitperforming the instruction, identification of registers used to supplydata for the corresponding data processing operation from among possibleregister files, and identification of the register destination of theresults of the corresponding data processing operation. As furtherexplained below, instructions can include a constant field in place ofone register number operand field. The result of this decoding aresignals for control of the target functional unit to perform the dataprocessing operation specified by the corresponding instruction on thespecified data.

Processing unit core 110 includes control registers 114. Controlregisters 114 store information for control of the functional units inscalar data path side A 115 and vector data path side B 116. Thisinformation may include mode information or the like.

The decoded instructions from instruction decode 113 and informationstored in control registers 114 are supplied to scalar data path side A115 and vector data path side B 116. As a result, functional unitswithin scalar data path side A 115 and vector data path side B 116perform instruction specified data processing operations uponinstruction specified data and store the results in an instructionspecified data register or registers. Each of scalar data path side A115 and vector data path side B 116 include multiple functional unitsthat operate in parallel. These are further described below inconjunction with FIG. 2. There is a data path 117 between scalar datapath side A 115 and vector data path side B 116 permitting dataexchange.

Processing unit core 110 includes further non-instruction-based modules.Emulation unit 118 permits determination of the machine state ofprocessing unit core 110 in response to instructions. This capabilitycan be employed for algorithmic development. Interrupts/exceptions unit119 enables processing unit core 110 to be responsive to external,asynchronous events (interrupts) and to respond to attempts to performimproper operations (exceptions).

Processor 100 includes streaming engine 125. Streaming engine 125supplies two data streams from predetermined addresses cached in L2combined cache 130 to register files of vector data path side B ofprocessing unit core 110. This provides controlled data movement frommemory (as cached in L2 combined cache 130) directly to functional unitoperand inputs. This is further described herein.

FIG. 1 illustrates example data widths of busses between various parts.L1I cache 121 supplies instructions to instruction fetch unit 111 viabus 141. Bus 141 is a 512-bit bus in this example. Bus 141 isunidirectional from L1I cache 121 to processing unit 110. L2 combinedcache 130 supplies instructions to L1I cache 121 via bus 142. Bus 142 isa 512-bit bus in this example. Bus 142 is unidirectional from L2combined cache 130 to L1I cache 121.

L1D cache 123 exchanges data with register files in scalar data pathside A 115 via bus 143. Bus 143 is a 64-bit bus in this example. L1Dcache 123 exchanges data with register files in vector data path side B116 via bus 144. Bus 144 is a 512-bit bus in this example. Busses 143and 144 are illustrated as bidirectional supporting both processing unitcore 110 data reads and data writes. L1D cache 123 exchanges data withL2 combined cache 130 via bus 145. Bus 145 is a 512-bit bus in thisexample. Bus 145 is illustrated as bidirectional supporting cacheservice for both processing unit core 110 data reads and data writes.

Processor data requests are directly fetched from L1D cache 123 upon acache hit (if the requested data is stored in L1D cache 123). Upon acache miss (the specified data is not stored in L1D cache 123), the datais sought in L2 combined cache 130. The memory locations of therequested data are either a hit in L2 combined cache 130 or a miss. Ahit is serviced from L2 combined cache 130. A miss is serviced fromanother level of cache (not illustrated) or from main memory (notillustrated). The requested data may be simultaneously supplied to bothL1D cache 123 and processing unit core 110 to speed use.

L2 combined cache 130 supplies data of a first data stream to streamingengine 125 via bus 146. Bus 146 is a 512-bit bus in this example.Streaming engine 125 supplies data of the first data stream tofunctional units of vector data path side B 116 via bus 147. Bus 147 isa 512-bit bus in this example. L2 combined cache 130 supplies data of asecond data stream to streaming engine 125 via bus 148. Bus 148 is a512-bit bus in this example. Streaming engine 125 supplies data of thissecond data stream to functional units of vector data path side B 116via bus 149, which is a 512-bit bus in this example. Busses 146, 147,148 and 149 are illustrated as unidirectional from L2 combined cache 130to streaming engine 125 and to vector data path side B 116 in accordancewith this example.

Streaming engine data requests are directly fetched from L2 combinedcache 130 upon a cache hit (if the requested data is stored in L2combined cache 130). Upon a cache miss (the specified data is not storedin L2 combined cache 130), the data is sought from another level ofcache (not illustrated) or from main memory (not illustrated). It istechnically feasible in some examples for L1D cache 123 to cache datanot stored in L2 combined cache 130. If such operation is supported,then upon a streaming engine data request that is a miss in L2 combinedcache 130, L2 combined cache 130 snoops L1D cache 123 for the streamingengine requested data. If L1D cache 123 stores the data, the snoopresponse includes the data, which is then supplied to service thestreaming engine request. If L1D cache 123 does not store the data, thesnoop response indicates this and L2 combined cache 130 services thestreaming engine request from another level of cache (not illustrated)or from main memory (not illustrated).

In this example, both L1D cache 123 and L2 combined cache 130 can beconfigured as selected amounts of cache or directly addressable memoryin accordance with U.S. Pat. No. 6,606,686 entitled UNIFIED MEMORYSYSTEM ARCHITECTURE INCLUDING CACHE AND DIRECTLY ADDRESSABLE STATICRANDOM ACCESS MEMORY, which is incorporated by reference herein.

In this example, processor 100 is fabricated on an integrated chip (IC)that is mounted on a ball grid array (BGA) substrate. A BGA substrateand IC die together may be referred to as “BGA package,” “IC package,”“integrated circuit,” “IC,” “chip,” “microelectronic device,” or similarterminology. The BGA package may include encapsulation material to coverand protect the IC die from damage. In another example, other types ofknown or later developed packaging techniques may be used with processor100.

FIG. 2 illustrates further details of functional units and registerfiles within scalar data path side A 115 and vector data path side B116. Scalar data path side A 115 includes L1 unit 221, S1 unit 222, M1unit 223, N1 unit 224, D1 unit 225 and D2 unit 226. Scalar data pathside A 115 includes global scalar register file 211, L1/S1 localregister file 212, M1/N1 local register file 213 and D1/D2 localregister file 214. Vector data path side B 116 includes L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit 246. Vectordata path side B 116 includes global vector register file 231, L2/S2local register file 232, M2/N2/C local register file 233 and predicateregister file 234. Which functional units can read from or write towhich register files is described in more detail herein.

Scalar data path side A 115 includes L1 unit 221. L1 unit 221 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or L1/S1 local register file 212.L1 unit 221 performs the following instruction selected operations:64-bit add/subtract operations; 32-bit min/max operations; 8-bit SingleInstruction Multiple Data (SIMD) instructions such as sum of absolutevalue, minimum and maximum determinations; circular min/max operations;and various move operations between register files. The result iswritten into an instruction specified register of global scalar registerfile 211, L1/S1 local register file 212, M1/N1 local register file 213or D1/D2 local register file 214.

Scalar data path side A 115 includes S1 unit 222. S1 unit 222 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or L1/S1 local register file 212.In this example, S1 unit 222 performs the same type operations as L1unit 221. In another example, there may be slight variations between thedata processing operations supported by L1 unit 221 and S1 unit 222. Theresult is written into an instruction specified register of globalscalar register file 211, L1/S1 local register file 212, M1/N1 localregister file 213 or D1/D2 local register file 214.

Scalar data path side A 115 includes M1 unit 223. M1 unit 223 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or M1/N1 local register file 213.In this example, M1 unit 223 performs the following instruction selectedoperations: 8-bit multiply operations; complex dot product operations;32-bit bit count operations; complex conjugate multiply operations; andbit-wise Logical Operations, moves, adds and subtracts. The result iswritten into an instruction specified register of global scalar registerfile 211, L1/S1 local register file 212, M1/N1 local register file 213or D1/D2 local register file 214.

Scalar data path side A 115 includes N1 unit 224. N1 unit 224 generallyaccepts two 64-bit operands and produces one 64-bit result. The twooperands are each recalled from an instruction specified register ineither global scalar register file 211 or M1/N1 local register file 213.In this example, N1 unit 224 performs the same type operations as M1unit 223. There are also double operations (called dual issuedinstructions) that employ both the M1 unit 223 and the N1 unit 224together. The result is written into an instruction specified registerof global scalar register file 211, L1/S1 local register file 212, M1/N1local register file 213 or D1/D2 local register file 214.

Scalar data path side A 115 includes D1 unit 225 and D2 unit 226. D1unit 225 and D2 unit 226 generally each accept two 64-bit operands andeach produce one 64-bit result. D1 unit 225 and D2 unit 226 generallyperform address calculations and corresponding load and storeoperations. D1 unit 225 is used for scalar loads and stores of 64 bits.D2 unit 226 is used for vector loads and stores of 512 bits. In thisexample, D1 unit 225 and D2 unit 226 also perform: swapping, pack andunpack on the load and store data; 64-bit SIMD arithmetic operations;and 64-bit bit-wise logical operations. D1/D2 local register file 214stores base and offset addresses used in address calculations for thecorresponding loads and stores. The two operands are each recalled froman instruction specified register in either global scalar register file211 or D1/D2 local register file 214. The calculated result is writteninto an instruction specified register of global scalar register file211, L1/S1 local register file 212, M1/N1 local register file 213 orD1/D2 local register file 214.

Vector data path side B 116 includes L2 unit 241. L2 unit 241 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231, L2/S2 local register file 232 orpredicate register file 234. In this example, L2 unit 241 performsinstruction similar to L1 unit 221 except on wider 512-bit data. Theresult may be written into an instruction specified register of globalvector register file 231, L2/S2 local register file 232, M2/N2/C localregister file 233 or predicate register file 234.

Vector data path side B 116 includes S2 unit 242. S2 unit 242 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231, L2/S2 local register file 232 orpredicate register file 234. In this example, S2 unit 242 performsinstructions similar to S1 unit 222. The result is written into aninstruction specified register of global vector register file 231, L2/S2local register file 232, M2/N2/C local register file 233 or predicateregister file 234.

Vector data path side B 116 includes M2 unit 243. M2 unit 243 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231 or M2/N2/C local register file233. In this example, M2 unit 243 performs instructions similar to M1unit 223 except on wider 512-bit data. The result is written into aninstruction specified register of global vector register file 231, L2/S2local register file 232 or M2/N2/C local register file 233.

Vector data path side B 116 includes N2 unit 244. N2 unit 244 generallyaccepts two 512-bit operands and produces one 512-bit result. The twooperands are each recalled from an instruction specified register ineither global vector register file 231 or M2/N2/C local register file233. In this example, N2 unit 244 performs the same type operations asM2 unit 243. There are also double operations (called dual issuedinstructions) that employ both M2 unit 243 and the N2 unit 244 together.The result is written into an instruction specified register of globalvector register file 231, L2/S2 local register file 232 or M2/N2/C localregister file 233.

Vector data path side B 116 includes correlation (C) unit 245. C unit245 generally accepts two 512-bit operands and produces one 512-bitresult. The two operands are each recalled from an instruction specifiedregister in either global vector register file 231 or M2/N2/C localregister file 233. In this example, C unit 245 performs “Rake” and“Search” instructions that are used for WCDMA (wideband code divisionmultiple access) encoding/decoding. In this example, C unit 245 canperform up to 512 multiples per clock cycle of a 2-bit PN (pseudorandomnumber) and 8-bit I/Q (complex number), 8-bit and 16-bitSum-of-Absolute-Difference (SAD) calculations, up to 512 SADs per clockcycle, horizontal add and horizontal min/max instructions, and vectorpermutes instructions. C unit 245 also contains 4 vector controlregisters (CUCR0 to CUCR3) used to control certain operations of C unit245 instructions. Control registers CUCR0 to CUCR3 are used as operandsin certain C unit 245 operations. In some examples, control registersCUCR0 to CUCR3 are used in control of a general permutation instruction(VPERM), and as masks for SIMD multiple DOT product operations (DOTPM)and SIMD multiple Sum-of-Absolute-Difference (SAD) operations. Infurther examples, control register CUCR0 is used to store thepolynomials for Galois Field Multiply operations (GFMPY) and controlregister CUCR1 is used to store the Galois field polynomial generatorfunction.

Vector data path side B 116 includes P unit 246. Vector predicate (P)unit 246 performs basic logic operations on registers of local predicateregister file 234. P unit 246 has direct access to read from and writeto predication register file 234. The logic operations include singleregister unary operations such as NEG (negate) which inverts each bit ofthe single register, BITCNT (bit count) which returns a count of thenumber of bits in the single register having a predetermined digitalstate (1 or 0), RMBD (right most bit detect) which returns a number ofbit positions from the least significant bit position (right most) to afirst bit position having a predetermined digital state (1 or 0),DECIMATE which selects every instruction specified Nth (1, 2, 4, etc.)bit to output, and EXPAND which replicates each bit an instructionspecified N times (2, 4, etc.). The logic operations also include tworegister binary operations such as AND which is a bitwise AND of data ofthe two registers, NAND which is a bitwise AND and negate of data of thetwo registers, OR which is a bitwise OR of data of the two registers,NOR which is a bitwise OR and negate of data of the two registers, andXOR which is exclusive OR of data of the two registers. The logicoperations include transfer of data from a predicate register ofpredicate register file 234 to another specified predicate register orto a specified data register in global vector register file 231. One useof P unit 246 is manipulation of the SIMD vector comparison results foruse in control of a further SIMD vector operation. The BITCNTinstruction can be used to count the number of 1's in a predicateregister to determine the number of valid data elements from a predicateregister.

FIG. 3 illustrates global scalar register file 211. There are 16independent 64-bit wide scalar registers designated A0 to A15. Eachregister of global scalar register file 211 can be read from or writtento as 64-bits of scalar data. All scalar data path side A 115 functionalunits (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225and D2 unit 226) can read or write to global scalar register file 211.Global scalar register file 211 can be read from as 32-bits or as64-bits and written to as 64-bits. The instruction executing determinesthe read data size. Vector data path side B 116 functional units (L2unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit246) can read from global scalar register file 211 via cross path 117under restrictions that are described below.

FIG. 4 illustrates D1/D2 local register file 214. There are sixteenindependent 64-bit wide scalar registers designated D0 to D16. Eachregister of D1/D2 local register file 214 is read from or written to as64-bits of scalar data. All scalar data path side A 115 functional units(L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2unit 226) can write to global scalar register file 211. Only D1 unit 225and D2 unit 226 can read from D1/D2 local scalar register file 214. Datastored in D1/D2 local scalar register file 214 can include baseaddresses and offset addresses used in address calculation.

FIG. 5 illustrates L1/S1 local register file 212. In this example, L1/S1local register file 212 includes eight independent 64-bit wide scalarregisters designated AL0 to AL7. In this example, the instruction codingpermits L1/S1 local register file 212 to include up to 16 registers. Inthis example, eight registers are implemented to reduce circuit size andcomplexity. Each register of L1/S1 local register file 212 can be readfrom or written to as 64-bits of scalar data. All scalar data path sideA 115 functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit224, D1 unit 225 and D2 unit 226) can write to L1/S1 local scalarregister file 212. L1 unit 221 and S1 unit 222 can read from L1/S1 localscalar register file 212.

FIG. 6 illustrates M1/N1 local register file 213. In this example, eightindependent 64-bit wide scalar registers designated AM0 to AM7 areimplemented. In this example, the instruction coding permits M1/N1 localregister file 213 to include up to 16 registers. In this example, eightregisters are implemented to reduce circuit size and complexity. Eachregister of M1/N1 local register file 213 can be read from or written toas 64-bits of scalar data. All scalar data path side A 115 functionalunits (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225and D2 unit 226) can write to M1/N1 local scalar register file 213. M1unit 223 and N1 unit 224 can read from M1/N1 local scalar register file213.

FIG. 7 illustrates global vector register file 231. There are sixteenindependent 512-bit wide vector registers. Each register of globalvector register file 231 can be read from or written to as 64-bits ofscalar data designated B0 to B15. Each register of global vectorregister file 231 can be read from or written to as 512-bits of vectordata designated VB0 to VB15. The instruction type determines the datasize. All vector data path side B 116 functional units (L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244, C unit 245 and P unit 246) can reador write to global vector register file 231. Scalar data path side A 115functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224, D1unit 225 and D2 unit 226) can read from global vector register file 231via cross path 117 under restrictions that are described below.

FIG. 8 illustrates predicate (P) local register file 234. There areeight independent 64-bit wide registers designated P0 to P7. Eachregister of P local register file 234 can be read from or written to as64-bits of scalar data. Vector data path side B 116 functional units L2unit 241, S2 unit 242, C unit 244 and P unit 246 can write to P localregister file 234. L2 unit 241, S2 unit 242 and P unit 246 can read fromP local scalar register file 234. One use of P local register file 234is writing one-bit SIMD vector comparison results from L2 unit 241, S2unit 242 or C unit 244, manipulation of the SIMD vector comparisonresults by P unit 246, and use of the manipulated results in control ofa further SIMD vector operation.

FIG. 9 illustrates L2/S2 local register file 232. In this example, eightindependent 512-bit wide vector registers are implemented. In thisexample, the instruction coding permits L2/S2 local register file 232 toinclude up to sixteen registers. In this example, eight registers areimplemented to reduce circuit size and complexity. Each register ofL2/S2 local vector register file 232 can be read from or written to as64-bits of scalar data designated BL0 to BL7. Each register of L2/S2local vector register file 232 can be read from or written to as512-bits of vector data designated VBL0 to VBL7. The instruction typedetermines the data size. All vector data path side B 116 functionalunits (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, C unit 245and P unit 246) can write to L2/S2 local vector register file 232. L2unit 241 and S2 unit 242 can read from L2/S2 local vector register file232.

FIG. 10 illustrates M2/N2/C local register file 233. In this example,eight independent 512-bit wide vector registers are implemented. In thisexample, the instruction coding permits M2/N2/C local register file 233to include up to sixteen registers. In this example, eight registers areimplemented to reduce circuit size and complexity. Each register ofM2/N2/C local vector register file 233 can be read from or written to as64-bits of scalar data designated BM0 to BM7. Each register of M2/N2/Clocal vector register file 233 can be read from or written to as512-bits of vector data designated VBM0 to VBM7. All vector data pathside B 116 functional units (L2 unit 241, S2 unit 242, M2 unit 243, N2unit 244, C unit 245 and P unit 246) can write to M2/N2/C local vectorregister file 233. M2 unit 243, N2 unit 244 and C unit 245 can read fromM2/N2/C local vector register file 233.

The provision of global register files accessible by all functionalunits of a side and local register files accessible by some of thefunctional units of a side is a design choice. In another example, adifferent accessibility provision could be made, such as employing onetype of register file corresponding to the global register filesdescribed herein.

Cross path 117 permits limited exchange of data between scalar data pathside A 115 and vector data path side B 116. During each operationalcycle one 64-bit data word can be recalled from global scalar registerfile A 211 for use as an operand by one or more functional units ofvector data path side B 116 and one 64-bit data word can be recalledfrom global vector register file 231 for use as an operand by one ormore functional units of scalar data path side A 115. Any scalar datapath side A 115 functional unit (L1 unit 221, S1 unit 222, M1 unit 223,N1 unit 224, D1 unit 225 and D2 unit 226) can read a 64-bit operand fromglobal vector register file 231. This 64-bit operand is the leastsignificant bits of the 512-bit data in the accessed register of globalvector register file 231. Multiple scalar data path side A 115functional units can employ the same 64-bit cross path data as anoperand during the same operational cycle. However, a single 64-bitoperand is transferred from vector data path side B 116 to scalar datapath side A 115 in a single operational cycle. Any vector data path sideB 116 functional unit (L2 unit 241, S2 unit 242, M2 unit 243, N2 unit244, C unit 245 and P unit 246) can read a 64-bit operand from globalscalar register file 211. If the corresponding instruction is a scalarinstruction, the cross-path operand data is treated as a 64-bit operand.If the corresponding instruction is a vector instruction, the upper 448bits of the operand are zero filled. Multiple vector data path side B116 functional units can employ the same 64-bit cross path data as anoperand during the same operational cycle. In one example, a single64-bit operand is transferred from scalar data path side A 115 to vectordata path side B 116 in a single operational cycle.

Streaming engine 125 (FIG. 1) transfers data in certain restrictedcircumstances. Streaming engine 125 controls two data streams. A streamincludes of a sequence of elements of a particular type. Programs thatoperate on streams read the data sequentially, operating on each elementin turn. Every stream has the following basic properties: the streamdata have a well-defined beginning and ending in time; the stream datahave fixed element size and type throughout the stream; and, the streamdata have a fixed sequence of elements. Once a stream is opened,streaming engine 125 performs the following operations: calculates theaddress; fetches the defined data type from L2 unified cache 130 (whichmay require cache service from a higher level memory, e.g., in the eventof a cache miss in L2); performs data type manipulation such as zeroextension, sign extension, data element sorting/swapping such as matrixtransposition; and delivers the data directly to the programmed dataregister file within processor core 110. Streaming engine 125 is thususeful for real-time digital filtering operations on well-behaved data.Streaming engine 125 frees the corresponding processor from these memoryfetch tasks, thus enabling other processing functions.

Streaming engine 125 provides several benefits. For example, streamingengine 125 permits multi-dimensional memory accesses, increases theavailable bandwidth to the functional units minimizes the number ofcache miss stalls since the stream buffer bypasses L1D cache 123, andreduces the number of scalar operations required to maintain a loop.Streaming engine 125 also manages address pointers and handles addressgeneration which frees up the address generation instruction slots andD1 unit 225 and D2 unit 226 for other computations.

Processor core 110 (FIG. 1) operates on an instruction pipeline.Instructions are fetched in instruction packets of fixed length asfurther described below. All instructions require the same number ofpipeline phases for fetch and decode but require a varying number ofexecute phases.

FIG. 11 illustrates the following pipeline phases: program fetch phase1110, dispatch and decode phases 1120, and execution phases 1130.Program fetch phase 1110 includes three stages for all instructions.Dispatch and decode phases 1120 include three stages for allinstructions. Execution phase 1130 includes one to four stages dependingon the instruction.

Fetch phase 1110 includes program address generation (PG) stage 1111,program access (PA) stage 1112 and program receive (PR) stage 1113.During program address generation stage 1111, the program address isgenerated in the processor and the read request is sent to the memorycontroller for the L1I cache. During the program access stage 1112, theL1I cache processes the request, accesses the data in its memory andsends a fetch packet to the processor boundary. During the programreceive stage 1113, the processor registers the fetch packet.

Instructions are fetched in a fetch packet that includes sixteen 32-bitwide words. FIG. 12 illustrates sixteen instructions 1201 to 1216 of asingle fetch packet. Fetch packets are aligned on 512-bit (16-word)boundaries. This example employs a fixed 32-bit instruction length whichenables decoder alignment. A properly aligned instruction fetch can loadmultiple instructions into parallel instruction decoders. Such aproperly aligned instruction fetch can be achieved by predeterminedinstruction alignment when stored in memory by having fetch packetsaligned on 512-bit boundaries coupled with a fixed instruction packetfetch. Conversely, variable length instructions require an initial stepof locating each instruction boundary before decoding. A fixed lengthinstruction set generally permits more regular layout of instructionfields which simplifies the construction of each decoder which is anadvantage for a wide issue VLIW processor.

The execution of the individual instructions is partially controlled bya p bit in each instruction. In this example, the p bit is bit 0 of the32-bit wide slot. The p bit determines whether an instruction executesin parallel with the next instruction. In this example, instructions arescanned from lower to higher address. If the p bit of an instruction is1, then the next following instruction (higher memory address) isexecuted in parallel with (in the same cycle as) that instruction. Ifthe p bit of an instruction is 0, then the next following instruction isexecuted in the cycle after the instruction.

Processor core 110 (FIG. 1) and L1I cache 121 pipelines (FIG. 1) arede-coupled from each other. Fetch packet returns from L1I cache can takea different number of clock cycles, depending on external circumstancessuch as whether there is a hit in L1I cache 121 or a hit in L2 combinedcache 130. Therefore, program access stage 1112 can take several clockcycles instead of one clock cycle as in the other stages.

The instructions executing in parallel constitute an execute packet. Inthis example, an execute packet can contain up to sixteen 32-bit wideslots for sixteen instructions. No two instructions in an execute packetcan use the same functional unit. A slot is one of five types: 1) aself-contained instruction executed on one of the functional units ofprocessor core 110 (L1 unit 221, S1 unit 222, M1 unit 223, N1 unit 224,D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit 243, N2 unit244, C unit 245 and P unit 246); 2) a unitless instruction such as a NOP(no operation) instruction or multiple NOP instructions; 3) a branchinstruction; 4) a constant field extension; and 5) a conditional codeextension. Some of these slot types are further explained herein.

Dispatch and decode phases 1120 (FIG. 11) include instruction dispatchto appropriate execution unit (DS) stage 1121, instruction pre-decode(DC1) stage 1122, and instruction decode, operand read (DC2) stage 1123.During instruction dispatch to appropriate execution unit stage 1121,the fetch packets are split into execute packets and assigned to theappropriate functional units. During the instruction pre-decode stage1122, the source registers, destination registers, and associated pathsare decoded for the execution of the instructions in the functionalunits. During the instruction decode, operand read stage 1123, moredetailed unit decodes are performed and operands are read from theregister files.

Execution phase 1130 includes execution (E1 to E5) stages 1131 to 1135.Different types of instructions require different numbers of such stagesto complete execution. The execution stages of the pipeline play animportant role in understanding the device state at processor cycleboundaries.

During E1 stage 1131, the conditions for the instructions are evaluatedand operands are operated on. As illustrated in FIG. 11, E1 stage 1131can receive operands from a stream buffer 1141 and one of the registerfiles shown schematically as 1142. For load and store instructions,address generation is performed, and address modifications are writtento a register file. For branch instructions, the branch fetch packet inPG phase is affected. As illustrated in FIG. 11, load and storeinstructions access memory here shown schematically as memory 1151. Forsingle-cycle instructions, results are written to a destination registerfile when any conditions for the instructions are evaluated as true. Ifa condition is evaluated as false, the instruction does not write anyresults or have any pipeline operation after E1 stage 1131.

During E2 stage 1132, load instructions send the address to memory.Store instructions send the address and data to memory. Single-cycleinstructions that saturate results set the SAT bit in the control statusregister (CSR) if saturation occurs. For 2-cycle instructions, resultsare written to a destination register file.

During E3 stage 1133, data memory accesses are performed. Any multiplyinstructions that saturate results set the SAT bit in the control statusregister (CSR) if saturation occurs. For 3-cycle instructions, resultsare written to a destination register file.

During E4 stage 1134, load instructions bring data to the processorboundary. For 4-cycle instructions, results are written to a destinationregister file.

During E5 stage 1135, load instructions write data into a register asillustrated schematically in FIG. 11 with input from memory 1151 to E5stage 1135.

FIG. 13 illustrates an example of the instruction coding 1300 offunctional unit instructions used by this example. Each instructionincludes 32 bits and controls the operation of one of the individuallycontrollable functional units (L1 unit 221, S1 unit 222, M1 unit 223, N1unit 224, D1 unit 225, D2 unit 226, L2 unit 241, S2 unit 242, M2 unit243, N2 unit 244, C unit 245 and P unit 246).

The creg field 1301 (bits 29 to 31) and the z bit 1302 (bit 28) areoptional fields used in conditional instructions. The bits are used forconditional instructions to identify the predicate register and thecondition. The z bit 1302 (bit 28) indicates whether the predication isbased upon zero or not zero in the predicate register. If z=1, the testis for equality with zero. If z=0, the test is for nonzero. The case ofcreg=0 and z=0 is treated as true to allow unconditional instructionexecution. The creg field 1301 and the z field 1302 are encoded in theinstruction as shown in Table 1.

TABLE 1 Conditional creg z Register 31 30 29 28 Unconditional 0 0 0 0Reserved 0 0 0 1 A0 0 0 1 z A1 0 1 0 z A2 0 1 1 z A3 1 0 0 z A4 1 0 1 zA5 1 1 0 z Reserved 1 1 x x

Execution of a conditional instruction is conditional upon the valuestored in the specified data register. The data register is in theglobal scalar register file 211 for all functional units. Note that “z”in the z bit column refers to the zero/not zero comparison selectionnoted above and “x” is a don't care state. This coding specifies asubset of the sixteen global registers as predicate registers whichpreserves bits in the instruction coding. Note that unconditionalinstructions do not have the optional bits. For unconditionalinstructions, the bits in fields 1301 and 1302 (28 to 31) are used asadditional opcode bits.

The dst field 1303 (bits 23 to 27) specifies a register in acorresponding register file as the destination of the instructionresults.

The src2/cst field 1304 (bits 18 to 22) has several meanings dependingon the instruction opcode field (bits 3 to 12 for all instructions andadditionally bits 28 to 31 for unconditional instructions). One meaningspecifies a register of a corresponding register file as the secondoperand. Another meaning is an immediate constant. Depending on theinstruction type, the field 1304 is treated as an unsigned integer andzero extended to a specified data length or is treated as a signedinteger and sign extended to the specified data length.

The src1 field 1305 (bits 13 to 17) specifies a register in acorresponding register file as the first source operand.

The opcode field 1306 (bits 3 to 12) for all instructions (andadditionally bits 28 to 31 for unconditional instructions) specifies thetype of instruction and designates appropriate instruction optionsincluding unambiguous designation of the functional unit used andoperation performed. A detailed explanation of the opcode is beyond thescope of this description except for the instruction options describedbelow.

The e bit 1307 (bit 2) is used for immediate constant instructions wherethe constant can be extended. If e=1, then the immediate constant isextended in a manner described below. If e=0, then the immediateconstant is not extended and the immediate constant is specified by thesrc2/cst field 1304 (bits 18 to 22). Note that the e bit 1307 is usedfor some instructions. Accordingly, with proper coding, the e bit 1307can be omitted from some instructions and the bit can be used as anadditional opcode bit.

The s bit 1308 (bit 1) designates scalar data path side A 115 or vectordata path side B 116. If s=0, then scalar data path side A 115 isselected which limits the functional unit to L1 unit 221, S1 unit 222,M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226 and thecorresponding register files illustrated in FIG. 2. Similarly, s=1selects vector data path side B 116 which limits the functional unit toL2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244, P unit 246 and thecorresponding register file illustrated in FIG. 2.

The p bit 1309 (bit 0) marks the execute packets. The p-bit determineswhether the instruction executes in parallel with the followinginstruction. The p-bits are scanned from lower to higher address. If p=1for the current instruction, then the next instruction executes inparallel with the current instruction. If p=0 for the currentinstruction, then the next instruction executes in the cycle after thecurrent instruction. All instructions executing in parallel constitutean execute packet. An execute packet can contain up to sixteeninstructions. Each instruction in an execute packet uses a differentfunctional unit.

There are two different condition code extension slots. Each executepacket can contain one each of these unique 32-bit condition codeextension slots which contains the 4-bit creg/z fields for theinstructions in the same execute packet. FIG. 14 illustrates the codingfor condition code extension slot 0 and FIG. 15 illustrates the codingfor condition code extension slot 1.

FIG. 14 illustrates the coding for condition code extension slot 0having 32 bits. Field 1401 (bits 28 to 31) specifies 4 creg/z bitsassigned to the L1 unit 221 instruction in the same execute packet.Field 1402 (bits 27 to 24) specifies four creg/z bits assigned to the L2unit 241 instruction in the same execute packet. Field 1403 (bits 20 to23) specifies four creg/z bits assigned to the S1 unit 222 instructionin the same execute packet. Field 1404 (bits 16 to 19) specifies fourcreg/z bits assigned to the S2 unit 242 instruction in the same executepacket. Field 1405 (bits 12 to 15) specifies four creg/z bits assignedto the D1 unit 225 instruction in the same execute packet. Field 1406(bits 8 to 11) specifies four creg/z bits assigned to the D2 unit 226instruction in the same execute packet. Field 1407 (bits 6 and 7) isunused/reserved. Field 1408 (bits 0 to 5) is coded as a set of uniquebits (CCEX0) to identify the condition code extension slot 0. Once theunique ID of condition code extension slot 0 is detected, thecorresponding creg/z bits are employed to control conditional executionof any L1 unit 221, L2 unit 241, S1 unit 222, S2 unit 242, D1 unit 225and D2 unit 226 instruction in the same execution packet. The creg/zbits are interpreted as shown in Table 1. If the correspondinginstruction is conditional (includes creg/z bits), the correspondingbits in the condition code extension slot 0 override the condition codebits in the instruction. Setting the creg/z bits equal to “0000” makesthe instruction unconditional. Thus, a properly coded condition codeextension slot 0 can make some corresponding instructions conditionaland some unconditional.

FIG. 15 illustrates the coding for condition code extension slot 1having 32 bits. Field 1501 (bits 28 to 31) specifies four creg/z bitsassigned to the M1 unit 223 instruction in the same execute packet.Field 1502 (bits 27 to 24) specifies four creg/z bits assigned to the M2unit 243 instruction in the same execute packet. Field 1503 (bits 19 to23) specifies four creg/z bits assigned to the C unit 245 instruction inthe same execute packet. Field 1504 (bits 16 to 19) specifies fourcreg/z bits assigned to the N1 unit 224 instruction in the same executepacket. Field 1505 (bits 12 to 15) specifies four creg/z bits assignedto the N2 unit 244 instruction in the same execute packet. Field 1506(bits 6 to 11) is unused/reserved. Field 1507 (bits 0 to 5) is coded asa set of unique bits (CCEX1) to identify the condition code extensionslot 1. Once the unique ID of condition code extension slot 1 isdetected, the corresponding creg/z bits are employed to controlconditional execution of any M1 unit 223, M2 unit 243, C unit 245, N1unit 224 and N2 unit 244 instruction in the same execution packet. Thesecreg/z bits are interpreted as shown in Table 1. If the correspondinginstruction is conditional (includes creg/z bits), the correspondingbits in the condition code extension slot 1 override the condition codebits in the instruction. Setting the creg/z bits equal to “0000” makesthe instruction unconditional. Thus, a properly coded condition codeextension slot 1 can make some instructions conditional and someunconditional.

Both condition code extension slot 0 and condition code extension slot 1can include a p bit to define an execute packet as described above inconjunction with FIG. 13. In this example, as illustrated in FIGS. 14and 15, code extension slot 0 and condition code extension slot 1 havebit 0 (p bit) encoded as 1. Thus, neither condition code extension slot0 nor condition code extension slot 1 can be in the last instructionslot of an execute packet.

There are two different 32-bit constant extension slots. Each executepacket can contain one each of the unique constant extension slots whichcontains 27 bits to be concatenated as high order bits with the 5-bitconstant field 1305 to form a 32-bit constant. As noted in theinstruction coding description above, some instructions define thesrc2/cst field 1304 as a constant rather than a source registeridentifier. At least some of such instructions can employ a constantextension slot to extend the constant to 32 bits.

FIG. 16 illustrates the fields of constant extension slot 0. Eachexecute packet can include one instance of constant extension slot 0 andone instance of constant extension slot 1. FIG. 16 illustrates thatconstant extension slot 0 1600 includes two fields. Field 1601 (bits 5to 31) constitutes the most significant 27 bits of an extended 32-bitconstant including the target instruction scr2/cst field 1304 as thefive least significant bits. Field 1602 (bits 0 to 4) is coded as a setof unique bits (CSTX0) to identify the constant extension slot 0. Inthis example, constant extension slot 0 1600 can be used to extend theconstant of one of an L1 unit 221 instruction, data in a D1 unit 225instruction, an S2 unit 242 instruction, an offset in a D2 unit 226instruction, an M2 unit 243 instruction, an N2 unit 244 instruction, abranch instruction, or a C unit 245 instruction in the same executepacket. Constant extension slot 1 is similar to constant extension slot0 except that bits 0 to 4 are coded as a set of unique bits (CSTX1) toidentify the constant extension slot 1. In this example, constantextension slot 1 can be used to extend the constant of one of an L2 unit241 instruction, data in a D2 unit 226 instruction, an S1 unit 222instruction, an offset in a D1 unit 225 instruction, an M1 unit 223instruction or an N1 unit 224 instruction in the same execute packet.

Constant extension slot 0 and constant extension slot 1 are used asfollows. The target instruction is of the type permitting constantspecification. In this example, the extension is implemented byreplacing one input operand register specification field with the leastsignificant bits of the constant as described above with respect toscr2/cst field 1304. Instruction decoder 113 determines this case, knownas an immediate field, from the instruction opcode bits. The targetinstruction also includes one constant extension bit (e bit 1307)dedicated to signaling whether the specified constant is not extended(constant extension bit=0) or extended (constant extension bit=1). Ifinstruction decoder 113 detects a constant extension slot 0 or aconstant extension slot 1, instruction decoder 113 further checks theother instructions within the execute packet for an instructioncorresponding to the detected constant extension slot. A constantextension is made if one corresponding instruction has a constantextension bit (e bit 1307) equal to 1.

FIG. 17 is a partial block diagram 1700 illustrating constant extension.FIG. 17 assumes that instruction decoder 113 (FIG. 1) detects a constantextension slot and a corresponding instruction in the same executepacket. Instruction decoder 113 supplies the twenty-seven extension bitsfrom the constant extension slot (bit field 1601) and the five constantbits (bit field 1305) from the corresponding instruction to concatenator1701. Concatenator 1701 forms a single 32-bit word from these two parts.In this example, the twenty-seven extension bits from the constantextension slot (bit field 1601) are the most significant bits and thefive constant bits (bit field 1305) are the least significant bits. Thecombined 32-bit word is supplied to one input of multiplexer 1702. Thefive constant bits from the corresponding instruction field 1305 supplya second input to multiplexer 1702. Selection of multiplexer 1702 iscontrolled by the status of the constant extension bit. If the constantextension bit (e bit 1307) is 1 (extended), multiplexer 1702 selects theconcatenated 32-bit input. If the constant extension bit is 0 (notextended), multiplexer 1702 selects the five constant bits from thecorresponding instruction field 1305. The output of multiplexer 1702supplies an input of sign extension unit 1703.

Sign extension unit 1703 forms the final operand value from the inputfrom multiplexer 1703. Sign extension unit 1703 receives control inputsScalar/Vector and Data Size. The Scalar/Vector input indicates whetherthe corresponding instruction is a scalar instruction or a vectorinstruction. The functional units of data path side A 115 (L1 unit 221,S1 unit 222, M1 unit 223, N1 unit 224, D1 unit 225 and D2 unit 226)perform scalar instructions. Any instruction directed to one of thesefunctional units is a scalar instruction. Data path side B functionalunits L2 unit 241, S2 unit 242, M2 unit 243, N2 unit 244 and C unit 245can perform scalar instructions or vector instructions. Instructiondecoder 113 determines whether the instruction is a scalar instructionor a vector instruction from the opcode bits. P unit 246 may performscalar instructions. The Data Size can be eight bits (byte B), sixteenbits (half-word H), 32 bits (word W), or 64 bits (double word D).

Table 2 lists the operation of sign extension unit 1703 for the variousoptions.

TABLE 2 Instruction Operand Constant Type Size Length Action ScalarB/H/W/D  5 bits Sign extend to 64 bits Scalar B/H/W/D 32 bits Signextend to 64 bits Vector B/H/W/D  5 bits Sign extend to operand size andreplicate across whole vector Vector B/H/W 32 bits Replicate 32-bitconstant across each 32-bit (W) lane Vector D 32 bits Sign extend to 64bits and replicate across each 64-bit (D) lane

Both constant extension slot 0 and constant extension slot 1 can includea p bit to define an execute packet as described above in conjunctionwith FIG. 13. In this example, as in the case of the condition codeextension slots, constant extension slot 0 and constant extension slot 1have bit 0 (p bit) encoded as 1. Thus, neither constant extension slot 0nor constant extension slot 1 can be in the last instruction slot of anexecute packet.

An execute packet can include a constant extension slot 0 or 1 and morethan one corresponding instruction marked constant extended (e bit=1).For such an occurrence, for constant extension slot 0, more than one ofan L1 unit 221 instruction, data in a D1 unit 225 instruction, an S2unit 242 instruction, an offset in a D2 unit 226 instruction, an M2 unit243 instruction or an N2 unit 244 instruction in an execute packet canhave an e bit of 1. For such an occurrence, for constant extension slot1, more than one of an L2 unit 241 instruction, data in a D2 unit 226instruction, an S1 unit 222 instruction, an offset in a D1 unit 225instruction, an M1 unit 223 instruction or an N1 unit 224 instruction inan execute packet can have an e bit of 1. In one example, instructiondecoder 113 determines that such an occurrence is an invalid operationand not supported. Alternately, the combination can be supported withextension bits of the constant extension slot applied to eachcorresponding functional unit instruction marked constant extended.

L1 unit 221, S1 unit 222, L2 unit 241, S2 unit 242 and C unit 245 oftenoperate in a single instruction multiple data (SIMD) mode. In this SIMDmode, the same instruction is applied to packed data from the twooperands. Each operand holds multiple data elements disposed inpredetermined slots. SIMD operation is enabled by carry control at thedata boundaries. Such carry control enables operations on varying datawidths.

FIG. 18 illustrates the carry control logic. AND gate 1801 receives thecarry output of bit N within the operand wide arithmetic logic unit (64bits for scalar data path side A 115 functional units and 512 bits forvector data path side B 116 functional units). AND gate 1801 alsoreceives a carry control signal which is further explained below. Theoutput of AND gate 1801 is supplied to the carry input of bit N+1 of theoperand wide arithmetic logic unit. AND gates such as AND gate 1801 aredisposed between every pair of bits at a possible data boundary. Forexample, for 8-bit data such an AND gate will be between bits 7 and 8,bits 15 and 16, bits 23 and 24, etc. Each such AND gate receives acorresponding carry control signal. If the data size is the minimumsize, each carry control signal is 0, effectively blocking carrytransmission between the adjacent bits. The corresponding carry controlsignal is 1 if the selected data size requires both arithmetic logicunit sections. Table 3 below shows example carry control signals for thecase of a 512-bit wide operand as used by vector data path side B 116functional units which can be divided into sections of 8 bits, 16 bits,32 bits, 64 bits, 128 bits or 256 bits. In Table 3, the upper 32 bitscontrol the upper bits (bits 128 to 511) carries and the lower 32 bitscontrol the lower bits (bits 0 to 127) carries. No control of the carryoutput of the most significant bit is needed, thus only 63 carry controlsignals are required.

TABLE 3 Data Size Carry Control Signals  8 bits (B) −000 0000 0000 00000000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 16 bits (H)−101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 0101 01010101 0101  32 bits (W) −111 0111 0111 0111 0111 0111 0111 0111 0111 01110111 0111 0111 0111 0111 0111 64 bits (D) −111 1111 0111 1111 0111 11110111 1111 0111 1111 0111 1111 0111 1111 0111 1111 128 bits −111 11111111 1111 0111 1111 1111 1111 0111 1111 1111 1111 0111 1111 1111 1111256 bits −111 1111 1111 1111 1111 1111 1111 1111 0111 1111 1111 11111111 1111 1111 1111

Operation on data sizes that are integral powers of 2 (2^(N)) is common.However, the carry control technique is not limited to integral powersof 2 and can be applied to other data sizes and operand widths.

In this example, at least L2 unit 241 and S2 unit 242 employ two typesof SIMD instructions using registers in predicate register file 234. Inthis example, the SIMD vector predicate instructions operate on aninstruction specified data size. The data sizes include byte (8 bit)data, half word (16 bit) data, word (32 bit) data, double word (64 bit)data, quad word (128 bit) data and half vector (256 bit) data. In thefirst of these instruction types, the functional unit (L unit 241 or Sunit 242) performs a SIMD comparison on packed data in two general dataregisters and supplies results to a predicate data register. Theinstruction specifies a data size, the two general data registeroperands, and the destination predicate register. In this example, eachpredicate data register includes one bit corresponding to each minimaldata size portion of the general data registers. In the current example,the general data registers are 512 bits (64 bytes) and the predicatedata registers are 64 bits (8 bytes). Each bit of a predicate dataregister corresponds to eight bits of a general data register. Thecomparison is performed on a specified data size (8, 16, 32, 64, 128 or256 bits). If the comparison is true, then the functional unit suppliesl's to all predicate register bits corresponding the that data sizeportion. If the comparison is false, the functional unit supplies zeroesto the predicate register bits corresponding to that data size portion.In this example, the enabled comparison operations include: less than,greater than, and equal to.

In the second of the instruction types, the functional unit (L2 unit 241or S2 unit 242) separately performs a first SIMD operation or a secondSIMD operation on packed data in general data registers based upon thestate of data in a predicate data register. The instruction specifies adata size, one or two general data register operands, a controllingpredicate register, and a general data register destination. Forexample, a functional unit can select, for each data sized portion oftwo vector operands, a first data element of a first operand or a seconddata element of a second operand dependent upon the I/O state ofcorresponding bits in the predicate data register to store in thedestination register. In another example, the data elements of a singlevector operand can be saved to memory or not saved dependent upon thedata of the corresponding bits of the predicate register.

The operations of P unit 245 permit a variety of compound vector SIMDoperations based upon more than one vector comparison. For example, arange determination can be made using two comparisons. In a SIMDoperation, a candidate vector is compared with a vector reference havingthe minimum of the range packed within a data register. The greater thanresult is scalar data with bits corresponding to the SIMD data width setto 0 or 1 depending upon the SIMD comparison and is stored in apredicate data register. Another SIMD comparison of the candidate vectoris performed with another reference vector having the maximum of therange packed within a different data register produces another scalarwith less than results stored in another predicate register. The P unitthen ANDs the two predicate registers. The AND result indicates whethereach SIMD data part of the candidate vector is within range or out ofrange. A P unit BITCNT instruction of the AND result can produce a countof the data elements within the comparison range. The P unit NEGfunction can be used to convert various expressions, such as: a lessthan comparison result to a greater than or equal comparison result; agreater than comparison result to a less than or equal to comparisonresult; or, an equal to comparison result to a not equal to comparisonresult.

Streaming Engine

FIG. 19 is a conceptual view of the streaming engine 125 of the exampleprocessor 100 of FIG. 1. FIG. 19 illustrates the processing of a singlestream representative of the two streams controlled by streaming engine125. Streaming engine 1900 includes stream address generator 1901.Stream address generator 1901 sequentially generates addresses of theelements of the stream and supplies these element addresses to systemmemory 1910. Memory 1910 recalls data stored at the element addresses(data elements) and supplies these data elements to datafirst-in-first-out (FIFO) buffer 1902. Data FIFO buffer 1902 providesbuffering between memory 1910 and processor 1920. Data formatter 1903receives the data elements from data FIFO memory 1902 and provides dataformatting according to the stream definition. This process is describedin more detail herein. Streaming engine 1900 supplies the formatted dataelements from data formatter 1903 to the processor 1920. A programexecuting on processor 1920 consumes the data and generates an output.

Stream elements typically reside in system memory. The memory imposes noparticular structure upon the stream. Programs define streams andthereby impose structure by specifying the stream attributes such asaddress of the first element of the stream, size and type of theelements in the stream, formatting for data in the stream, and theaddress sequence associated with the stream.

The streaming engine defines an address sequence for elements of thestream in terms of a pointer walking through memory. A multiple-levelnested loop controls the path the pointer takes. An iteration count fora loop level indicates the number of times the level repeats. Adimension gives the distance between pointer positions of the looplevel.

In a basic forward stream, the innermost loop consumes physicallycontiguous elements from memory as the implicit dimension of theinnermost loop is one element. The pointer moves from element to elementin consecutive, increasing order. In each level outside the inner loop,that loop moves the pointer to a new location based on the size of thedimension of the loop level.

This form of addressing allows programs to specify regular paths throughmemory using a small number of parameters. Table 4 lists the addressingparameters of a basic stream.

TABLE 4 Parameter Definition ELEM_BYTES Size of each element in bytesICNT0 Number of iterations for the innermost loop level 0. At loop level0 all elements are physically contiguous. Implied DIM0 = ELEM_BYTESICNT1 Number of iterations for loop level 1 DIM1 Number of bytes betweenthe starting points for consecutive iterations of loop level 1 ICNT2Number of iterations for loop level 2 DIM2 Number of bytes between thestarting points for consecutive iterations of loop level 2 ICNT3 Numberof iterations for loop level 3 DIM3 Number of bytes between the startingpoints for consecutive iterations of loop level 3 ICNT4 Number ofiterations for loop level 4 DIM4 Number of bytes between the startingpoints for consecutive iterations of loop level 4 ICNT5 Number ofiterations for loop level 5 DIM5 Number of bytes between the startingpoints for consecutive iterations of loop level 5

In this example, ELEM_BYTES ranges from 1 to 64 bytes as shown in Table5.

TABLE 5 ELEM_BYTES Stream Element Length 000 1 byte 001 2 bytes 010 4bytes 011 8 bytes 100 16 bytes 101 32 bytes 110 64 bytes 111 Reserved

The definition above maps consecutive elements of the stream toincreasing addresses in memory which is appropriate for many algorithms.Some algorithms are better served by reading elements in decreasingmemory address order or reverse stream addressing. For example, adiscrete convolution computes vector dot-products, as illustrated byexpression (1).(f*g)[t]=Σ_(x=−∞) ^(∞) f[x]g[t−x]  (1)

In expression (1), f[ ] and g[ ] represent arrays in memory. For eachoutput, the algorithm reads f[ ] in the forward direction and reads g[ ]in the reverse direction. Practical filters limit the range of indicesfor [x] and [t−x] to a finite number of elements. To support thispattern, the streaming engine supports reading elements in decreasingaddress order.

Matrix multiplication presents a unique problem to the streaming engine.Each element in the matrix product is a vector dot product between a rowfrom the first matrix and a column from the second. Programs typicallystore matrices in row-major or column-major order. Row-major orderstores all the elements of a single row contiguously in memory.Column-major order stores all elements of a single column contiguouslyin memory. Matrices are typically stored in the same order as thedefault array order for the language. As a result, only one of the twomatrices in a matrix multiplication map on to the 2-dimensional streamdefinition of the streaming engine. In a typical example, an index stepsthrough columns on one array and rows of the other array. The streamingengine supports implicit matrix transposition with transposed streams.Transposed streams avoid the cost of explicitly transforming the data inmemory. Instead of accessing data in strictly consecutive-element order,the streaming engine effectively interchanges the inner two loopdimensions of the traversal order, fetching elements along the seconddimension into contiguous vector lanes.

This algorithm works but is impractical to implement for small elementsizes. Some algorithms work on matrix tiles which are multiple columnsand rows together. Therefore, the streaming engine defines a separatetransposition granularity. The hardware imposes a minimum granularity.The transpose granularity needs to be at least as large as the elementsize. Transposition granularity causes the streaming engine to fetch oneor more consecutive elements from dimension 0 before moving alongdimension 1. When the granularity equals the element size, a singlecolumn from a row-major array is fetched. Otherwise, the granularityspecifies fetching two, four or more columns at a time from a row-majorarray. This is also applicable for column-major layout by exchanging rowand column in the description. A parameter GRANULE indicates thetransposition granularity in bytes.

Another common matrix multiplication technique exchanges the innermosttwo loops of the matrix multiply. The resulting inner loop no longerreads down the column of one matrix while reading across the row ofanother. For example, the algorithm may hoist one term outside the innerloop, replacing it with the scalar value. The innermost loop can beimplemented with a single scalar by vector multiply followed by a vectoradd. Or, the scalar value can be duplicated across the length of thevector and a vector by vector multiply used. The streaming engine ofthis example directly supports the latter case and related use modelswith an element duplication mode. In this mode, the streaming enginereads a granule smaller than the full vector size and replicates thatgranule to fill the next vector output.

The streaming engine treats each complex number as a single element withtwo sub-elements that give the real and imaginary (rectangular) ormagnitude and angle (polar) portions of the complex number. Not allprograms or peripherals agree what order these sub-elements shouldappear in memory. Therefore, the streaming engine offers the ability toswap the two sub-elements of a complex number with no cost. The featureswaps the halves of an element without interpreting the contents of theelement and can be used to swap pairs of sub-elements of any type, notjust complex numbers.

Algorithms generally prefer to work at high precision, but highprecision values require more storage and bandwidth than lower precisionvalues. Commonly, programs store data in memory at low precision,promote those values to a higher precision for calculation, and thendemote the values to lower precision for storage. The streaming enginesupports such operations directly by allowing algorithms to specify onelevel of type promotion. In this example, every sub-element can bepromoted to a larger type size with either sign or zero extension forinteger types. In some examples, the streaming engine supports floatingpoint promotion, promoting 16-bit and 32-bit floating point values to32-bit and 64-bit formats, respectively.

While the streaming engine defines a stream as a discrete sequence ofdata elements, the processing unit core 110 consumes data elementspacked contiguously in vectors. The vectors resemble streams as thevectors contain multiple homogeneous elements with some implicitsequence. Because the streaming engine reads streams, but the processingunit core 110 consumes vectors, the streaming engine maps streams ontovectors in a consistent way.

Vectors include equal-sized lanes, each lane containing a sub-element.The processing unit core 110 designates the rightmost lane of the vectoras lane 0, regardless of current endian mode. Lane numbers increaseright-to-left. The actual number of lanes within a vector variesdepending on the length of the vector and the data size of thesub-element.

FIG. 20 illustrates the sequence of the formatting operations offormatter 1903. Formatter 1903 includes three sections: input section2010, formatting section 2020, and output section 2030. Input section2010 receives the data recalled from system memory 1910 as accessed bystream address generator 1901. The data can be via linear fetch stream2011 or transposed fetch stream 2012.

Formatting section 2020 includes various formatting blocks. Theformatting performed within formatter 1903 by the blocks is furtherdescribed below. Complex swap block 2021 optionally swaps twosub-elements forming a complex number element. Type promotion block 2022optionally promotes each data element into a larger data size. Promotionincludes zero extension for unsigned integers and sign extension forsigned integers. Decimation block 2023 optionally decimates the dataelements. In this example, decimation can be 2:1 retaining every otherdata element or 4:1 retaining every fourth data element. Elementduplication block 2024 optionally duplicates individual data elements.In this example, the data element duplication is an integer power of 2(2N, where N is an integer) including 2×, 4×, 8×, 16×, 32× and 64×. Inthis example, data duplication can extend over multiple destinationvectors. Vector length masking/group duplication block 2025 has twoprimary functions. An independently specified vector length VECLENcontrols the data elements supplied to each output data vector. Whengroup duplication is off, excess lanes in the output data vector arezero filled and these lanes are marked invalid. When group duplicationis on, input data elements of the specified vector length are duplicatedto fill the output data vector.

Output section 2030 holds the data for output to the correspondingfunctional units. Register and buffer for processor 2031 stores aformatted vector of data to be used as an operand by the functionalunits of processing unit core 110 (FIG. 1).

FIG. 21 illustrates an example of lane allocation in a vector. Vector2100 is divided into eight 64-bit lanes (8×64 bits=512 bits, the vectorlength). Lane 0 includes bits 0 to 63, line 1 includes bits 64 to 127,lane 2 includes bits 128 to 191, lane 3 includes bits 192 to 255, lane 4includes bits 256 to 319, lane 5 includes bits 320 to 383, lane 6includes bits 384 to 447. and lane 7 includes bits 448 to 511.

FIG. 22 illustrates another example of lane allocation in a vector.Vector 2210 is divided into sixteen 32-bit lanes (16×32 bits=512 bits,the vector length). Lane 0 includes bits 0 to 31, line 1 includes bits32 to 63, lane 2 includes bits 64 to 95, lane 3 includes bits 96 to 127,lane 4 includes bits 128 to 159, lane 5 includes bits 160 to 191, lane 6includes bits 192 to 223, lane 7 includes bits 224 to 255, lane 8includes bits 256 to 287, lane 9 includes bits 288 to 319, lane 10includes bits 320 to 351, lane 11 includes bits 352 to 383, lane 12includes bits 384 to 415, lane 13 includes bits 416 to 447, lane 14includes bits 448 to 479, and lane 15 includes bits 480 to 511.

The streaming engine maps the innermost stream dimension directly tovector lanes. The streaming engine maps earlier elements within theinnermost stream dimension to lower lane numbers and later elements tohigher lane numbers, regardless of whether the stream advances inincreasing or decreasing address order. Whatever order the streamdefines, the streaming engine deposits elements in vectors inincreasing-lane order. For non-complex data, the streaming engine placesthe first element in lane 0 of the vector processing unit core 110(FIG. 1) fetches, the second in lane 1, and so on. For complex data, thestreaming engine places the first element in lanes 0 and 1, the secondelement in lanes 2 and 3, and so on. Sub-elements within an elementretain the same relative ordering regardless of the stream direction.For non-swapped complex elements, the sub-elements with the loweraddress of each pair are placed in the even numbered lanes, and thesub-elements with the higher address of each pair are placed in the oddnumbered lanes. For swapped complex elements, the placement is reversed.

The streaming engine fills each vector processing unit core 110 fetcheswith as many elements as possible from the innermost stream dimension.If the innermost dimension is not a multiple of the vector length, thestreaming engine zero pads the dimension to a multiple of the vectorlength. As noted below, the streaming engine also marks the lanesinvalid. Thus, for higher-dimension streams, the first element from eachiteration of an outer dimension arrives in lane 0 of a vector. Thestreaming engine maps the innermost dimension to consecutive lanes in avector. For transposed streams, the innermost dimension includes groupsof sub-elements along dimension 1, not dimension 0, as transpositionexchanges these two dimensions.

Two-dimensional (2D) streams exhibit greater variety as compared toone-dimensional streams. A basic 2D stream extracts a smaller rectanglefrom a larger rectangle. A transposed 2D stream reads a rectanglecolumn-wise instead of row-wise. A looping stream, where the seconddimension overlaps first, executes a finite impulse response (FIR)filter taps which loops repeatedly over FIR filter samples providing asliding window of input samples.

FIG. 23 illustrates a region of memory that can be accessed using abasic two-dimensional stream. The inner two dimensions, represented byELEM_BYTES, ICNT0, DIM1 and ICNT1 (refer to Table 4), give sufficientflexibility to describe extracting a smaller rectangle 2320 havingdimensions 2321 and 2322 from a larger rectangle 2310 having dimensions2311 and 2312. In this example, rectangle 2320 is a 9 by 13 rectangle of64-bit values and rectangle 2310 is a larger 11 by 19 rectangle. Thefollowing stream parameters define this stream: ICNT0=9, ELEM_BYTES=8,ICNT1=13, and DIM1=88 (11 times 8).

Thus, the iteration count in the 0-dimension 2321 is nine and theiteration count in the 1-dimension 2322 is thirteen. Note that theELEM_BYTES scales the innermost dimension. The first dimension has ICNT0elements of size ELEM_BYTES. The stream address generator does not scalethe outer dimensions. Therefore, DIM1=88, which is eleven elementsscaled by eight bytes per element.

FIG. 24 illustrates the order of elements within the example stream ofFIG. 23. The streaming engine fetches elements for the stream in theorder illustrated in order 2400. The first nine elements come from thefirst row of rectangle 2320, left-to-right in hops 1 to 8. The 10ththrough 24th elements comes from the second row, and so on. When thestream moves from the 9th element to the 10th element (hop 9 in FIG.24), the streaming engine computes the new location based on theposition of the pointer at the start of the inner loop, not the positionof the pointer at the end of the first dimension. Thus, DIM1 isindependent of ELEM_BYTES and ICNT0. DIM1 represents the distancebetween the first bytes of each consecutive row.

Transposed streams are accessed along dimension 1 before dimension 0.The following examples illustrate transposed streams with varyingtransposition granularity. FIG. 25 illustrates extracting a smallerrectangle 2520 (12×8) having dimensions 2521 and 2522 from a largerrectangle 2510 (14×13) having dimensions 2511 and 2512. In FIG. 25,ELEM_BYTES equal 2.

FIG. 26 illustrates how the streaming engine fetches the stream of theexample stream of FIG. 25 with a transposition granularity of fourbytes. Fetch pattern 2600 fetches pairs of elements from each row(because the granularity of four is twice the ELEM_BYTES of two), butotherwise moves down the columns. Once the streaming engine reaches thebottom of a pair of columns, the streaming engine repeats the patternwith the next pair of columns.

FIG. 27 illustrates how the streaming engine fetches the stream of theexample stream of FIG. 25 with a transposition granularity of eightbytes. The overall structure remains the same. The streaming enginefetches four elements from each row (because the granularity of eight isfour times the ELEM_BYTES of two) before moving to the next row in thecolumn as shown in fetch pattern 2700.

The streams examined so far read each element from memory exactly once.A stream can read a given element from memory multiple times, in effectlooping over a portion of memory. FIR filters exhibit two common loopingpatterns: re-reading the same filter taps for each output and readinginput samples from a sliding window. Two consecutive outputs need inputsfrom two overlapping windows.

FIG. 28 illustrates the details of streaming engine 125 of FIG. 1.Streaming engine 125 contains three major sections: Stream 0 engine2810; Stream 1 engine 2820; and Shared L2 Interfaces 2830. Stream 0engine 2810 and Stream 1 2820 both contain identical hardware thatoperates in parallel. Stream 0 engine 2810 and Stream 1 engine 2820 bothshare L2 interfaces 2830. Each stream 0 engine 2810 and stream 1 engine2820 provides processing unit core 110 (FIG. 1) data at a rate of up to512 bits/cycle, every cycle, which is enabled by the dedicated streampaths and shared dual L2 interfaces.

Each streaming engine 125 includes a respective dedicated 6-dimensional(6D) stream address generator 2811/2821 that can each generate one newnon-aligned request per cycle. As is further described herein, addressgenerators 2811/2821 output 512-bit aligned addresses that overlap theelements in the sequence defined by the stream parameters.

Each address generator 2811/2821 connects to a respective dedicatedmicro table look-aside buffer (μTLB) 2812/2822. The TLB 2812/2822converts a single 48-bit virtual address to a 44-bit physical addresseach cycle. Each μTLB 2812/2822 has 8 entries, covering a minimum of 32kB with 4 kB pages or a maximum of 16 MB with 2 MB pages. Each addressgenerator 2811/2821 generates 2 addresses per cycle. The μTLB 2812/2822only translates one address per cycle. To maintain throughput, streamingengine 125 operates under the assumption that most stream references arewithin the same 4 kB page. Thus, the address translation does not modifybits 0 to 11 of the address. If aout0 and aout1 line in the same 4 kBpage (aout0[47:12] are the same aout1[47:12]), then the μTLB 2812/2822only translates aout0 and reuses the translation for the upper bits ofboth addresses.

Translated addresses are queued in respective command queue 2813/2823.These addresses are aligned with information from the respectivecorresponding Storage Allocation and Tracking block 2814/2824. Streamingengine 125 does not explicitly manage tTLB 2812/2822. The system memorymanagement unit (MMU) invalidates μTLBs as necessary during contextswitches.

Storage Allocation and Tracking 2814/2824 manages the internal storageof the stream, discovering data reuse and tracking the lifetime of eachpiece of data. The block accepts two virtual addresses per cycle andbinds those addresses to slots in the internal storage. The data storeis organized as an array of slots. The streaming engine maintainsfollowing metadata to track the contents and lifetime of the data ineach slot: 49-bit virtual address associated with the slot, valid bitindicating valid address, ready bit indicating data has arrived for theaddress, active bit indicating if there are any references outstandingto this data, and a last reference value indicating the most recentreference to this slot in the reference queue. The storage allocationand tracking are further described herein.

Respective reference queue 2815/2825 stores the sequence of referencesgenerated by the respective corresponding address generator 2811/2821.The reference sequence enables the data formatting network to presentdata to processing unit core 110 in the correct order. Each entry inrespective reference queue 2815/2825 contains the information necessaryto read data out of the data store and align the data for processingunit core 110. Respective reference queue 2815/2825 maintains theinformation listed in Table 6 in each slot.

TABLE 6 Data Slot Low Slot number for the lower half of data associatedwith aout0 Data Slot High Slot number for the upper half of dataassociated with aout1 Rotation Number of bytes to rotate data to alignnext element with lane 0 Length Number of valid bytes in this reference

Storage allocation and tracking 2814/2824 inserts references inreference queue 2815/2825 as address generator 2811/2821 generates newaddresses. Storage allocation and tracking 2814/2824 removes referencesfrom reference queue 2815/2825 when the data becomes available and thereis room in the stream head registers. As storage allocation and tracking2814/2824 removes slot references from reference queue 2815/2825 andformats data, the references are checked for the last reference to thecorresponding slots. Storage allocation and tracking 2814/2824 comparesreference queue 2815/2825 removal pointer against the recorded lastreference of the slot. If the pointer and the recorded last referencematch, then storage allocation and tracking 2814/2824 marks the slotinactive once the data is no longer needed.

Streaming engine 125 has respective data storage 2816/2826 for aselected number of elements. Deep buffering allows the streaming engineto fetch far ahead in the stream, hiding memory system latency. Eachdata storage 2816/2826 accommodates two simultaneous read operations andtwo simultaneous write operations per cycle and each is thereforereferred to a two-read, two-write (2r2w) data storage. In otherexamples, the amount of buffering can be different. In the currentexample, streaming engine 125 dedicates 32 slots to each stream witheach slot tagged by a virtual address. Each slot holds 64 bytes of datain eight banks of eight bytes.

Data storage 2816/2826 and the respective storage allocation/trackinglogic 2814/2824 and reference queues 2815/2825 implement the data FIFO1902 discussed with reference to FIG. 19.

Respective butterfly network 2817/2827 includes a seven-stage butterflynetwork that implements the formatter 1903 (FIG. 19, FIG. 20). Butterflynetwork 2817/2827 receives 128 bytes of input and generates 64 bytes ofoutput. The first stage of the butterfly is actually a half-stage thatcollects bytes from both slots that match a non-aligned fetch and mergesthe collected bytes into a single, rotated 64-byte array. The remainingsix stages form a standard butterfly network. Respective butterflynetwork 2817/2827 performs the following operations: rotates the nextelement down to byte lane 0; promotes data types by a power of two, ifrequested; swaps real and imaginary components of complex numbers, ifrequested; and converts big endian to little endian if processing unitcore 110 is presently in big endian mode. The user specifies elementsize, type promotion, and real/imaginary swap as part of the parametersof the stream.

Streaming engine 125 attempts to fetch and format data ahead ofprocessing unit core 110's demand in order to maintain full throughput.Respective stream head registers 2818/2828 provide a small amount ofbuffering so that the process remains fully pipelined. Respective streamhead registers 2818/2828 are not directly architecturally visible. Eachstream also has a respective stream valid register 2819/2829. Validregisters 2819/2829 indicate which elements in the corresponding streamhead registers 2818/2828 are valid. The outputs of stream head registers2818/2828 and valid registers 2819/2829 are provided to processing unitcore 110 via buses 2840/2841.

The two streams 2810/2820 share a pair of independent L2 interfaces2830: L2 Interface A (IFA) 2833 and L2 Interface B (IFB) 2834. Each L2interface provides 512 bits/cycle throughput direct to the L2 controller130 (FIG. 1) via respective buses 147/149 for an aggregate bandwidth of1024 bits/cycle. The L2 interfaces use the credit-based multicore busarchitecture (MBA) protocol. The MBA protocol is described in moredetail in U.S. Pat. No. 9,904,645, “Multicore Bus Architecture withNon-Blocking High Performance Transaction Credit System,” which isincorporated by reference herein. The L2 controller assigns a pool ofcommand credits to each interface. The pool has sufficient credits sothat each interface can send sufficient requests to achieve fullread-return bandwidth when reading L2 RAM, L2 cache and multicore sharedmemory controller (MSMC) memory, as described in more detail herein.

To maximize performance, in this example both streams can use both L2interfaces, allowing a single stream to send a peak command rate of tworequests per cycle. Each interface prefers one stream over the other,but this preference changes dynamically from request to request. IFA2833 and IFB 2834 prefer opposite streams, when IFA 2833 prefers Stream0, IFB 2834 prefers Stream 1 and vice versa.

Respective arbiter 2831/2832 ahead of each respective interface2833/2834 applies the following basic protocol on every cycle havingcredits available. Arbiter 2831/2832 checks if the preferred stream hasa command ready to send. If so, arbiter 2831/2832 chooses that command.Arbiter 2831/2832 next checks if an alternate stream has at least tworequests ready to send, or one command and no credits. If so, arbiter2831/2832 pulls a command from the alternate stream. If either interfaceissues a command, the notion of preferred and alternate streams swap forthe next request. Using this algorithm, the two interfaces dispatchrequests as quickly as possible while retaining fairness between the twostreams. The first rule ensures that each stream can send a request onevery cycle that has available credits. The second rule provides amechanism for one stream to borrow the interface of the other when thesecond interface is idle. The third rule spreads the bandwidth demandfor each stream across both interfaces, ensuring neither interfacebecomes a bottleneck.

Respective coarse grain rotator 2835/2836 enables streaming engine 125to support a transposed matrix addressing mode. In this mode, streamingengine 125 interchanges the two innermost dimensions of themultidimensional loop to access an array column-wise rather thanrow-wise. Respective rotators 2835/2836 are not architecturally visible.

FIG. 29 illustrates an example stream template register 2900. The streamdefinition template provides the full structure of a stream thatcontains data. The iteration counts and dimensions provide most of thestructure, while the various flags provide the rest of the details. Inthis example, a single stream template 2900 is defined for alldata-containing streams. All stream types supported by the streamingengine are covered by the template 2900. The streaming engine supports asix-level loop nest for addressing elements within the stream. Most ofthe fields in the stream template 2900 map directly to the parameters inthat algorithm. The numbers above the fields are bit numbers within a256-bit vector. Table 7 shows the stream field definitions of a streamtemplate.

TABLE 7 FIG. 29 Reference Size Field Name Number Description Bits ICNT02901 Iteration count for loop 0 32 ICNT1 2902 Iteration count for loop 132 ICNT2 2903 Iteration count for loop 2 32 ICNT3 2904 Iteration countfor loop 3 32 ICNT4 2905 Iteration count for loop 4 32 INCT5 2906Iteration count for loop 5 32 DIM1 2911 Signed dimension for loop 1 32DIM2 2912 Signed dimension for loop 2 32 DIM3 2913 Signed dimension forloop 3 32 DIM4 2914 Signed dimension for loop 4 32 DIM5 2915 Signeddimension for loop 5 32 FLAGS 2921 Stream modifier flags 64

Loop 0 is the innermost loop and loop 5 is the outermost loop. In thecurrent example, DIM0 is equal to ELEM_BYTES defining physicallycontiguous data. Thus, the stream template register 2900 does not defineDIM0. Streaming engine 125 interprets iteration counts as unsignedintegers and dimensions as unscaled signed integers. An iteration countof zero at any level (ICNT0, ICNT1, ICNT2, ICNT3, ICNT4 or ICNT5)indicates an empty stream. Each iteration count must be at least one todefine a valid stream. The template above specifies the type ofelements, length and dimensions of the stream. The stream instructionsseparately specify a start address, e.g., by specification of a scalarregister in scalar register file 211 which stores the start address.Thus, a program can open multiple streams using the same template butdifferent registers storing the start address.

FIG. 30 illustrates an example of sub-field definitions of the flagsfield 2921 shown in FIG. 29. As shown in FIG. 30, the flags field 2911is 6 bytes or 48 bits. FIG. 30 shows bit numbers of the fields. Table 8shows the definition of these fields.

TABLE 8 FIG. 30 Reference Size Field Name Number Description Bits ELTYPE3001 Type of data element 4 TRANSPOSE 3002 Two dimensional transposemode 3 PROMOTE 3003 Promotion mode 3 VECLEN 3004 Stream vector length 3ELDUP 3005 Element duplication 3 GRDUP 3006 Group duplication 1 DECIM3007 Element decimation 2 THROTTLE 3008 Fetch ahead throttle mode 2DIMFMT 3009 Stream dimensions format 3 DIR 3010 Stream direction 1 0forward direction 1 reverse direction CBK0 3011 First circular blocksize number 4 CBK1 3012 Second circular block size number 4 AM0 3013Addressing mode for loop 0 2 AM1 3014 Addressing mode for loop 1 2 AM23015 Addressing mode for loop 2 2 AM3 3016 Addressing mode for loop 3 2AM4 3017 Addressing mode for loop 4 2 AM5 3018 Addressing mode for loop5 2

The Element Type (ELTYPE) field 3001 defines the data type of theelements in the stream. The coding of the four bits of the ELTYPE field3001 is defined as shown in Table 9.

TABLE 9 Sub-element Total Element ELTYPE Real/Complex Size Bits SizeBits 0000 real 8 8 0001 real 16 16 0010 real 32 32 0011 real 64 64 0100reserved 0101 reserved 0110 reserved 0111 reserved 1000 complex no swap8 16 1001 complex no swap 16 32 1010 complex no swap 32 64 1011 complexno swap 64 128 1100 complex swapped 8 16 1101 complex swapped 16 32 1110complex swapped 32 64 1111 complex swapped 64 128

Real/Complex Type determines whether the streaming engine treats eachelement as a real number or two parts (real/imaginary ormagnitude/angle) of a complex number and also specifies whether to swapthe two parts of complex numbers. Complex types have a total elementsize twice the sub-element size. Otherwise, the sub-element size equalsthe total element size.

Sub-Element Size determines the type for purposes of type promotion andvector lane width. For example, 16-bit sub-elements get promoted to32-bit sub-elements or 64-bit sub-elements when a stream requests typepromotion. The vector lane width matters when processing unit core 110(FIG. 1) operates in big endian mode, as the core 110 lays out vectorsin little endian order.

Total Element Size specifies the minimal granularity of the stream whichdetermines the number of bytes the stream fetches for each iteration ofthe innermost loop. Streams read whole elements, either in increasing ordecreasing order. Therefore, the innermost dimension of a stream spansICNT0×total-element-size bytes.

The TRANSPOSE field 3002 determines whether the streaming engineaccesses the stream in a transposed order. The transposed orderexchanges the inner two addressing levels. The TRANSPOSE field 3002 alsoindicated the granularity for transposing the stream. The coding of thethree bits of the TRANSPOSE field 3002 is defined as shown in Table 10for normal 2D operations.

TABLE 10 Transpose Meaning 000 Transpose disabled 001 Transpose on 8-bitboundaries 010 Transpose on 16-bit boundaries 011 Transpose on 32-bitboundaries 100 Transpose on 64-bit boundaries 101 Transpose on 128-bitboundaries 110 Transpose on 256-bit boundaries 111 Reserved

Streaming engine 125 can transpose data elements at a differentgranularity than the element size thus allowing programs to fetchmultiple columns of elements from each row. The transpose granularitycannot be smaller than the element size. The TRANSPOSE field 3002interacts with the DIMFMT field 3009 in a manner further describedbelow.

The PROMOTE field 3003 controls whether the streaming engine promotessub-elements in the stream and the type of promotion. When enabled,streaming engine 125 promotes types by powers-of-2 sizes. The coding ofthe three bits of the PROMOTE field 3003 is defined as shown in Table11.

TABLE 11 Promotion Promotion Resulting Sub-element Size PROMOTE FactorType 8-bit 16-bit 32-bit 64-bit 000 1x N/A  8-bit 16-bit 32-bit 64-bit001 2x zero 16-bit 32-bit 64-bit Invalid extend 010 4x zero 32-bit64-bit Invalid Invalid extend 011 8x zero 64-bit Invalid Invalid Invalidextend 100 reserved 101 2x sign 16-bit 32-bit 64-bit Invalid extend 1104x sign 32-bit 64-bit Invalid Invalid extend 111 8x sign 64-bit InvalidInvalid Invalid extend

When PROMOTE is 000, corresponding to a 1× promotion, each sub-elementis unchanged and occupies a vector lane equal in width to the sizespecified by ELTYPE. When PROMOTE is 001, corresponding to a 2×promotion and zero extend, each sub-element is treated as an unsignedinteger and zero extended to a vector lane twice the width specified byELTYPE. A 2× promotion is invalid for an initial sub-element size of 64bits. When PROMOTE is 010, corresponding to a 4× promotion and zeroextend, each sub-element is treated as an unsigned integer and zeroextended to a vector lane four times the width specified by ELTYPE. A 4×promotion is invalid for an initial sub-element size of 32 or 64 bits.When PROMOTE is 011, corresponding to an 8× promotion and zero extend,each sub-element is treated as an unsigned integer and zero extended toa vector lane eight times the width specified by ELTYPE. An 8× promotionis invalid for an initial sub-element size of 16, 32 or 64 bits. WhenPROMOTE is 101, corresponding to a 2× promotion and sign extend, eachsub-element is treated as a signed integer and sign extended to a vectorlane twice the width specified by ELTYPE. A 2× promotion is invalid foran initial sub-element size of 64 bits. When PROMOTE is 110,corresponding to a 4× promotion and sign extend, each sub-element istreated as a signed integer and sign extended to a vector lane fourtimes the width specified by ELTYPE. A 4× promotion is invalid for aninitial sub-element size of 32 or 64 bits. When PROMOTE is 111,corresponding to an 8× promotion and zero extend, each sub-element istreated as a signed integer and sign extended to a vector lane eighttimes the width specified by ELTYPE. An 8× promotion is invalid for aninitial sub-element size of 16, 32 or 64 bits.

The VECLEN field 3004 defines the stream vector length for the stream inbytes. Streaming engine 125 breaks the stream into groups of elementsthat are VECLEN bytes long. The coding of the three bits of the VECLENfield 3004 is defined as shown in Table 12.

TABLE 12 VECLEN Stream Vector Length 000 1 byte 001 2 bytes 010 4 bytes011 8 bytes 100 16 bytes 101 32 bytes 110 64 bytes 111 Reserved

VECLEN cannot be less than the product of the element size in bytes andthe duplication factor. As shown in Table 11, the maximum VECLEN of 64bytes equals the preferred vector size of vector data path side B 116.When VECLEN is shorter than the native vector width of processing unitcore 110, streaming engine 125 pads the extra lanes in the vectorprovided to processing unit core 110. The GRDUP field 3006 determinesthe type of padding. The VECLEN field 3004 interacts with ELDUP field3005 and GRDUP field 3006 in a manner detailed below.

The ELDUP field 3005 specifies the number of times to duplicate eachelement. The element size multiplied with the element duplication amountcannot exceed the 64 bytes. The coding of the three bits of the ELDUPfield 3005 is defined as shown in Table 13.

TABLE 13 ELDUP Duplication Factor 000 No Duplication 001 2 times 010 4times 011 8 times 100 16 times 101 32 times 110 64 times 111 Reserved

The ELDUP field 3005 interacts with VECLEN field 3004 and GRDUP field3006 in a manner detailed below. The nature of the relationship betweenthe permitted element size, the element duplication factor, and thedestination vector length requires that a duplicated element thatoverflows the first destination register fills an integer number ofdestination registers upon completion of duplication. The data of theadditional destination registers eventually supplies the respectivestream head register 2818/2828. Upon completion of duplication of afirst data element, the next data element is rotated down to the leastsignificant bits of source register 3100 discarding the first dataelement. The process then repeats for the new data element.

The GRDUP bit 3006 determines whether group duplication is enabled. IfGRDUP bit 3006 is 0, then group duplication is disabled. If the GRDUPbit 3006 is 1, then group duplication is enabled. When enabled by GRDUPbit 3006, streaming engine 125 duplicates a group of elements to fillthe vector width. VECLEN field 3004 defines the length of the group toreplicate. When VECLEN field 3004 is less than the vector length ofprocessing unit core 110 and GRDUP bit 3006 enables group duplication,streaming engine 125 fills the extra lanes (see FIGS. 21 and 22) withadditional copies of the stream vector. Because stream vector length andvector length of processing unit core 110 are integral powers of two,group duplication produces an integral number of duplicate copies. NoteGRDUP and VECLEN do not specify the number of duplications. The numberof duplications performed is based upon the ratio of VECLEN to thenative vector length, which is 64 bytes/512 bits in this example.

The GRDUP field 3006 specifies how streaming engine 125 pads streamvectors for bits following the VECLEN length to the vector length ofprocessing unit core 110. When GRDUP bit 3006 is 0, streaming engine 125fills the extra lanes with zeros and marks the extra vector lanesinvalid. When GRDUP bit 3006 is 1, streaming engine 125 fills extralanes with copies of the group of elements in each stream vector.Setting GRDUP bit 3006 to 1 has no effect when VECLEN is set to thenative vector width of processing unit core 110. VECLEN must be at leastas large as the product of ELEM_BYTES and the element duplication factorELDUP. That is, an element or the duplication factor number of elementscannot be separated using VECLEN.

Group duplication operates to the destination vector size. Groupduplication does not change the data supplied when the product of theelement size ELEM_BYTES and element duplication factor ELDUP equals orexceeds the destination vector width. Under such conditions, the statesof the GRDUP bit 3006 and the VECLEN field 3004 have no effect on thesupplied data.

The set of examples below illustrate the interaction between VECLEN andGRDUP. Each of the following examples show how the streaming engine mapsa stream onto vectors across different stream vector lengths and thevector size of vector data path side B 116. The stream of this exampleincludes twenty-nine elements (E0 to E28) of 64 bits/8 bytes. The streamcan be a linear stream of twenty-nine elements or an inner loop of 29elements. The tables illustrate eight byte lanes such as shown in FIG.21. Each illustrated vector is stored in the respective stream headregister 2818/2828 in turn.

Table 14 illustrates how the example stream maps onto bits within the64-byte processor vectors when VECLEN is 64 bytes.

TABLE 14 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E7 E6 E5 E4 E3 E2 E1 E0 2 E15 E14 E13 E12 E11 E10 E9 E8 3E23 E22 E21 E20 E19 E18 E17 E16 4 0 0 0 E28 E27 E26 E25 E24

As shown in Table 14, the stream extends over four vectors. Aspreviously described, the lanes within vector 4 that extend beyond thestream are zero filled. When VECLEN has a size equal to the nativevector length, the value of GRDUP does not matter as no duplication cantake place with such a VECLEN.

Table 15 shows the same parameters as shown in Table 14, except withVECLEN of 32 bytes. Group duplicate is disabled (GRDUP=0).

TABLE 15 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 E3 E2 E1 E0 2 0 0 0 0 E7 E6 E5 E4 3 0 0 0 0 E11 E10E9 E8 4 0 0 0 0 E15 E14 E13 E12 5 0 0 0 0 E19 E18 E17 E16 6 0 0 0 0 E23E22 E21 E20 7 0 0 0 0 E27 E26 E25 E24 8 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream are distributed over lanes 0 to 3in eight vectors. Extra lanes 4 to 7 in vectors 1-7 are zero filled. Invector 8, lane 1 has a stream element (E28) and the other lanes are zerofilled.

Table 16 shows the same parameters as shown in Table 14, except withVECLEN of sixteen bytes. Group duplicate is disabled (GRDUP=0).

TABLE 16 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 0 0 E1 E0 2 0 0 0 0 0 0 E3 E2 3 0 0 0 0 0 0 E5 E4 40 0 0 0 0 0 E7 E6 5 0 0 0 0 0 0 E9 E8 6 0 0 0 0 0 0 E11 E10 7 0 0 0 0 00 E13 E12 8 0 0 0 0 0 0 E15 E14 9 0 0 0 0 0 0 E17 E16 10 0 0 0 0 0 0 E19E18 11 0 0 0 0 0 0 E21 E20 12 0 0 0 0 0 0 E23 E22 13 0 0 0 0 0 0 E25 E2414 0 0 0 0 0 0 E27 E26 15 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream are distributed over lane 0 andlane 1 in fifteen vectors. Extra lanes 2 to 7 in vectors 1-14 are zerofilled. In vector 15, lane 1 has a stream element (E28) and the otherlanes are zero filled.

Table 17 shows the same parameters as shown in Table 14, except withVECLEN of eight bytes. Group duplicate is disabled (GRDUP=0).

TABLE 17 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 0 0 0 0 0 0 0 E0 2 0 0 0 0 0 0 0 E1 3 0 0 0 0 0 0 0 E2 4 0 00 0 0 0 0 E3 5 0 0 0 0 0 0 0 E4 6 0 0 0 0 0 0 0 E5 7 0 0 0 0 0 0 0 E6 80 0 0 0 0 0 0 E7 9 0 0 0 0 0 0 0 E8 10 0 0 0 0 0 0 0 E9 11 0 0 0 0 0 0 0E10 12 0 0 0 0 0 0 0 E11 13 0 0 0 0 0 0 0 E12 14 0 0 0 0 0 0 0 E13 15 00 0 0 0 0 0 E14 16 0 0 0 0 0 0 0 E15 17 0 0 0 0 0 0 0 E16 18 0 0 0 0 0 00 E17 19 0 0 0 0 0 0 0 E18 20 0 0 0 0 0 0 0 E19 21 0 0 0 0 0 0 0 E20 220 0 0 0 0 0 0 E21 23 0 0 0 0 0 0 0 E22 24 0 0 0 0 0 0 0 E23 25 0 0 0 0 00 0 E24 26 0 0 0 0 0 0 0 E25 27 0 0 0 0 0 0 0 E26 28 0 0 0 0 0 0 0 E2729 0 0 0 0 0 0 0 E28

The twenty-nine elements of the stream appear in lane 0 in twenty-ninevectors. Extra lanes 1-7 in vectors 1-29 are zero filled.

Table 18 shows the same parameters as shown in Table 15, except withVECLEN of thirty-two bytes and group duplicate is enabled (GRDUP=1).

TABLE 18 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E3 E2 E1 E0 E3 E2 E1 E0 2 E7 E6 E5 E4 E7 E6 E5 E4 3 E11 E10E9 E8 E11 E10 E9 E8 4 E15 E14 E13 E12 E15 E14 E13 E12 5 E19 E18 E17 E16E19 E18 E17 E16 6 E23 E22 E21 E20 E23 E22 E21 E20 7 E27 E26 E25 E24 E27E26 E25 E24 8 0 0 0 E28 0 0 0 E28

The twenty-nine elements of the stream are distributed over lanes 0-7 ineight vectors. Each vector 1-7 includes four elements duplicated. Theduplication factor (2) results because VECLEN (32 bytes) is half thenative vector length of 64 bytes. In vector 8, lane 0 has a streamelement (E28) and lanes 1-3 are zero filled. Lanes 4-7 of vector 9duplicate this pattern.

Table 19 shows the same parameters as shown in Table 16, except withVECLEN of sixteen bytes. Group duplicate is enabled (GRDUP=1).

TABLE 19 processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E1 E0 E1 E0 E1 E0 E1 E0 2 E3 E2 E3 E2 E3 E2 E3 E2 3 E5 E4 E5E4 E5 E4 E5 E4 4 E7 E6 E7 E6 E7 E6 E7 E6 5 E9 E8 E9 E8 E9 E8 E9 E8 6 E11E10 E11 E10 E11 E10 E11 E10 7 E13 E12 E13 E12 E13 E12 E13 E12 8 E15 E14E15 E14 E15 E14 E15 E14 9 E17 E16 E17 E16 E17 E16 E17 E16 10 E19 E18 E19E18 E19 E18 E19 E18 11 E21 E20 E21 E20 E21 E20 E21 E20 12 E23 E22 E23E22 E23 E22 E23 E22 13 E25 E24 E25 E24 E25 E24 E25 E24 14 E27 E26 E27E26 E27 E26 E27 E26 15 0 E28 0 E28 0 E28 0 E28

The twenty-nine elements of the stream are distributed over lanes 0-7 infifteen vectors. Each vector 1-7 includes two elements duplicated fourtimes. The duplication factor (4) results because VECLEN (16 bytes) isone quarter the native vector length of 64 bytes. In vector 15, lane 0has a stream element (E28) and lane 1 is zero filled. This pattern isduplicated in lanes 2 and 3, lanes 4 and 5, and lanes 6 and 7 of vector15.

Table 20 shows the same parameters as shown in Table 17, except withVECLEN of eight bytes. Group duplicate is enabled (GRDUP=1).

TABLE 20 Processor Lane Lane Lane Lane Lane Lane Lane Lane Vectors 7 6 54 3 2 1 0 1 E0 E0 E0 E0 E0 E0 E0 E0 2 E1 E1 E1 E1 E1 E1 E1 E1 3 E2 E2 E2E2 E2 E2 E2 E2 4 E3 E3 E3 E3 E3 E3 E3 E3 5 E4 E4 E4 E4 E4 E4 E4 E4 6 E5E5 E5 E5 E5 E5 E5 E5 7 E6 E6 E6 E6 E6 E6 E6 E6 8 E7 E7 E7 E7 E7 E7 E7 E79 E8 E8 E8 E8 E8 E8 E8 E8 10 E9 E9 E9 E9 E9 E9 E9 E9 11 E10 E10 E10 E10E10 E10 E10 E10 12 E11 E11 E11 E11 E11 E11 E11 E11 13 E12 E12 E12 E12E12 E12 E12 E12 14 E13 E13 E13 E13 E13 E13 E13 E13 15 E14 E14 E14 E14E14 E14 E14 E14 16 E15 E15 E15 E15 E15 E15 E15 E15 17 E16 E16 E16 E16E16 E16 E16 E16 18 E17 E17 E17 E17 E17 E17 E17 E17 19 E18 E18 E18 E18E18 E18 E18 E18 20 E19 E19 E19 E19 E19 E19 E19 E19 21 E20 E20 E20 E20E20 E20 E20 E20 22 E21 E21 E21 E21 E21 E21 E21 E21 23 E22 E22 E22 E22E22 E22 E22 E22 24 E23 E23 E23 E23 E23 E23 E23 E23 25 E24 E24 E24 E24E24 E24 E24 E24 26 E25 E25 E25 E25 E25 E25 E25 E25 27 E26 E26 E26 E26E26 E26 E26 E26 28 E27 E27 E27 E27 E27 E27 E27 E27 29 E28 E28 E28 E28E28 E28 E28 E28

The twenty-nine elements of the stream all appear on lanes 0 to 7 intwenty-nine vectors. Each vector includes one element duplicated eighttimes. The duplication factor (8) results because VECLEN (8 bytes) isone eighth the native vector length of 64 bytes. Thus, each lane is thesame in vectors 1-29.

FIG. 31 illustrates an example of vector length masking/groupduplication block 2025 (see FIG. 20) that is included within formatterblock 1903 of FIG. 19. Input register 3100 receives a vector input fromelement duplication block 2024 shown in FIG. 20. Input register 3100includes 64 bytes arranged in 64 1-byte blocks byte0 to byte63. Notethat bytes byte0 to byte63 are each equal in length to the minimum ofELEM_BYTES. A set of multiplexers 3101 to 3163 couple input bytes fromsource register 3100 to output register 3170. Each respectivemultiplexer 3101 to 3163 supplies an input to a respective byte1 tobyte63 of output register 3170. Not all input bytes byte0 to byte63 ofinput register 3100 are coupled to every multiplexer 3101 to 3163. Notethere is no multiplexer supplying byte0 of output register 3170. In thisexample, byte0 of output register 3170 is supplied by byte0 of inputregister 3100.

Multiplexers 3101 to 3163 are controlled by multiplexer control encoder3180. Multiplexer control encoder 3180 receives ELEM_BYTES, VECLEN andGRDUP input signals and generates respective control signals formultiplexers 3101 to 3163. ELEM_BYTES and ELDUP are supplied tomultiplexer control encoder 3180 to check to see that VECLEN is at leastas great as the product of ELEM_BYTES and ELDUP. In operation,multiplexer control encoder 3180 controls multiplexers 3101 to 3163 totransfer least significant bits equal in number to VECLEN from inputregister 3100 to output register 3170. If GRDUP=0 indicating groupduplication disabled, then multiplexer control encoder 3180 controls theremaining multiplexers 3101 to 3163 to transfer zeros to all bits in theremaining most significant lanes of output register 3170. If GRDUP=1indicating group duplication enabled, then multiplexer control encoder3180 controls the remaining multiplexers 3101 to 3163 to duplicate theVECLEN number of least significant bits of input register 3100 into themost significant lanes of output register 3170. This control is similarto the element duplication control described above and fills the outputregister 3170 with the first vector. For the next vector, data withininput register 3100 is rotated down by VECLEN, discarding the previousVECLEN least significant bits. The rate of data movement in formatter1903 (FIG. 19) is set by the rate of consumption of data by processingunit core 110 (FIG. 1) via stream read and advance instructionsdescribed below. The group duplication formatting repeats as long as thestream includes additional data elements.

Element duplication (ELDUP) and group duplication (GRUDP) areindependent. Note these features include independent specification andparameter setting. Thus, element duplication and group duplication canbe used together or separately. Because of how these are specified,element duplication permits overflow to the next vector while groupduplication does not.

Referring again to FIG. 30, the DECIM field 3007 controls data elementdecimation of the corresponding stream. Streaming engine 125 deletesdata elements from the stream upon storage in respective stream headregisters 2818/2828 for presentation to the requesting functional unit.Decimation removes whole data elements, not sub-elements. The DECIMfield 3007 is defined as listed in Table 21.

TABLE 21 DECIM Decimation Factor 00 No Decimation 01 2 times 10 4 times11 Reserved

If DECIM field 3007 equals 00, then no decimation occurs. The dataelements are passed to the corresponding stream head registers 2818/2828without change. If DECIM field 3007 equals 01, then 2:1 decimationoccurs. Streaming engine 125 removes odd number elements from the datastream upon storage in the stream head registers 2818/2828. Limitationsin the formatting network require 2:1 decimation to be employed withdata promotion by at least 2× (PROMOTE cannot be 000), ICNT0 must bemultiple of 2, and the total vector length (VECLEN) must be large enoughto hold a single promoted, duplicated element. For transposed streams(TRANSPOSE 0), the transpose granule must be at least twice the elementsize in bytes before promotion. If DECIM field 3007 equals 10, then 4:1decimation occurs. Streaming engine 125 retains every fourth dataelement removing three elements from the data stream upon storage in thestream head registers 2818/2828. Limitations in the formatting networkrequire 4:1 decimation to be employed with data promotion by at least 4×(PROMOTE cannot be 000, 001 or 101), ICNT0 must be a multiple of 4 andthe total vector length (VECLEN) must be large enough to hold a singlepromoted, duplicated element. For transposed streams (TRANSPOSE≠0), inone example, decimation removes columns, and does not remove rows. Thus,in such cases, the transpose granule must be at least twice the elementsize in bytes before promotion for 2:1 decimation (GRANULE≥2×ELEM_BYTES)and at least four times the element size in bytes before promotion for4:1 decimation (GRANULE≥4×ELEM_BYTES).

The THROTTLE field 3008 controls how aggressively the streaming enginefetches ahead of processing unit core 110. The coding of the two bits ofthis field is defined as shown in Table 22.

TABLE 22 THROTTLE Description 00 Minimum throttling, maximum fetch ahead01 Less throttling, more fetch ahead 10 More throttling, less fetchahead 11 Maximum throttling, minimum fetch ahead

THROTTLE does not change the meaning of the stream and serves only as ahint. The streaming engine can ignore this field. Programs should notrely on the specific throttle behavior for program correctness, becausethe architecture does not specify the precise throttle behavior.THROTTLE allows programmers to provide hints to the hardware about theprogram behavior. By default, the streaming engine attempts to get asfar ahead of processing unit core 110 as possible to hide as muchlatency as possible (equivalent to THROTTLE=11), while providing fullstream throughput to processing unit core 110. While some applicationsneed this level of throughput, such throughput can cause bad systemlevel behavior for others. For example, the streaming engine discardsall fetched data across context switches. Therefore, aggressivefetch-ahead can lead to wasted bandwidth in a system with large numbersof context switches.

The DIMFMT field 3009 defines which of the loop count fields ICNT0 2901,ICNT1 2902, ICNT2 2903, ICNT3 2804, ICNT4 2905 and ICNT5 2906, of theloop dimension fields DIM1 2911, DIM2 2912, DIM3 2913, DIM4 2914 andDIM5 2915 and of the addressing mode fields AM0 3013, AM1 3014, AM23015, AM3 3016, AM4 3017 and AM5 3018 (part of FLAGS field 2921) of thestream template register 2900 are active for the particular stream.Table 23 lists the active loops for various values of the DIMFMT field3009. Each active loop count must be at least 1 and the outer activeloop count must be greater than 1.

TABLE 23 DIMFMT Loop5 Loop4 Loop3 Loop2 Loop1 Loop0 000 InactiveInactive Inactive Inactive Inactive Active 001 Inactive InactiveInactive Inactive Active Active 010 Inactive Inactive Inactive ActiveActive Active 011 Inactive Inactive Active Active Active Active 100Inactive Active Active Active Active Active 101 Active Active ActiveActive Active Active 110-111 Reserved

The DIR bit 3010 determines the direction of fetch of the inner loop(Loop0). If the DIR bit 3010 is 0, Loop0 fetches are in the forwarddirection toward increasing addresses. If the DIR bit 3010 is 1, Loop0fetches are in the backward direction toward decreasing addresses. Thefetch direction of other loops is determined by the sign of thecorresponding loop dimension DIM1, DIM2, DIM3, DIM4 and DIM5.

The CBK0 field 3011 and the CBK1 field 3012 control the circular blocksize upon selection of circular addressing. The manner of determiningthe circular block size is described herein.

The AM0 field 3013, AM1 field 3014, AM2 field 3015, AM3 field 3016, AM4field 3017 and AM5 field 3018 control the addressing mode of acorresponding loop, thus permitting the addressing mode to beindependently specified for each loop. Each of AM0 field 3013, AM1 field3014, AM2 field 3015, AM3 field 3016, AM4 field 3017 and AM5 field 3018are three bits and are decoded as listed in Table 24.

TABLE 24 AMx field Meaning 00 Linear addressing 01 Circular addressingblock size set by CBK0 10 Circular addressing block size set by CBK0 +CBK1 + 1 11 reserved

In linear addressing, the address advances according to the addressarithmetic whether forward or reverse. In circular addressing, theaddress remains within a defined address block. Upon reaching the end ofthe circular address block the address wraps around to the beginninglimit of the block. Circular addressing blocks are limited to 2Naddresses where N is an integer. Circular address arithmetic can operateby cutting the carry chain between bits and not allowing a selectednumber of most significant bits to change. Thus, arithmetic beyond theend of the circular block changes only the least significant bits. Theblock size is set as listed in Table 25.

TABLE 25 Encoded Block Size CBK0 or CBK0 + CBK1 + 1 Block Size (bytes) 0512 1  1K 2  2K 3  4K 4  8K 5  16K 6  32K 7  64K 8 128K 9 256K 10 512K11  1M 12  2M 13  4M 14  8M 15  16M 16  32M 17  64M 18 128M 19 256M 20512M 21  1 G 22  2 G 23  4 G 24  8 G 25  16 G 26  32 G 27  64 G 28Reserved 29 Reserved 30 Reserved 31 Reserved

In this example, the circular block size is set by the number encoded byCBK0 (first circular address mode 01) or the number encoded byCBK0+CBK1+1 (second circular address mode 10). For example, in the firstcircular address mode, the circular address block size can range from512 bytes to 16 M bytes. For the second circular address mode, thecircular address block size can range from 1 K bytes to 64 G bytes.Thus, the encoded block size is 2^((B+9)) bytes, where B is the encodedblock number which is CBK0 for the first block size (AMx of 01) andCBK0+CBK1+1 for the second block size (AMx of 10).

The processing unit 110 (FIG. 1) exposes the streaming engine 125 (FIG.28) to programs through a small number of instructions and specializedregisters. Programs start and end streams with SEOPEN and SECLOSE.SEOPEN opens a new stream and the stream remains open until terminatedexplicitly by SECLOSE or replaced by a new stream with SEOPEN. TheSEOPEN instruction specifies a stream number indicating opening stream 0or stream 1. The SEOPEN instruction specifies a data register storingthe start address of the stream. The SEOPEN instruction also specifies astream template register that stores the stream template as describedabove. The arguments of the SEOPEN instruction are listed in Table 26.

TABLE 26 Argument Description Stream Start Address Scalar registerstoring stream start address Register Stream Number Stream 0 or Stream 1Stream Template Vector register storing stream template data Register

The stream start address register is a register in general scalarregister file 211 (FIG. 2) in this example. The SEOPEN instruction canspecify the stream start address register via scr1 field 1305 (FIG. 13)of example instruction coding 1300 (FIG. 13). The SEOPEN instructionspecifies stream 0 or stream 1 in the opcode. The stream templateregister is a vector register in general vector register file 221 inthis example. The SEOPEN instruction can specify the stream templateregister via scr2/cst field 1304 (FIG. 13). If the specified stream isactive, the SEOPEN instruction closes the prior stream and replaces thestream with the specified stream.

SECLOSE explicitly marks a stream inactive, flushing any outstandingactivity. Any further references to the stream trigger exceptions.SECLOSE also allows a program to prematurely terminate one or bothstreams.

An SESAVE instruction saves the state of a stream by capturingsufficient state information of a specified stream to restart thatstream in the future. An SERSTR instruction restores a previously savedstream. An SESAVE instruction saves the stream metadata and does notsave any of the stream data. The stream re-fetches stream data inresponse to an SERSTR instruction.

Each stream can be in one of three states: inactive, active, or frozenafter reset. Both streams begin in the inactive state. Opening a streammoves the stream to the active state. Closing the stream returns thestream to the inactive state. In the absence of interrupts andexceptions, streams ordinarily do not make other state transitions. Toaccount for interrupts, the streaming engine adds a third state: frozen.The frozen state represents an interrupted active stream.

In this example, four bits, two bits per stream, define the state ofboth streams. One bit per stream resides within the streaming engine,and the other bit resides within the processor core 110. The streamingengine internally tracks whether each stream holds a parameter setassociated with an active stream. This bit distinguishes an inactivestream from a not-inactive stream. The processor core 110 separatelytracks the state of each stream with a dedicated bit per stream in theTask State Register (TSR): TSR.SE0 for stream 0, and TSR.SE1 forstream 1. These bits distinguish between active and inactive streams.

Opening a stream moves the stream to the active state. Closing a streammoves the stream to the inactive state. If a program opens a new streamover a frozen stream, the new stream replaces the old stream and thestreaming engine discards the contents of the previous stream. Thestreaming engine supports opening a new stream on a currently activestream. The streaming engine discards the contents of the previousstream, flushes the pipeline, and starts fetching data for the newopened stream. Data to processor is asserted once the data has returned.If a program closes an already closed stream, nothing happens. If aprogram closes an open or frozen stream, the streaming engine discardsall state related to the stream, clears the internal stream-active bit,and clears the counter, tag and address registers. Closing a streamserves two purposes. Closing an active stream allows a program tospecifically state the stream and the resources associated with thestream are no longer needed. Closing a frozen stream also allows contextswitching code to clear the state of the frozen stream, so that othertasks do not see it.

As noted above, there are circumstances when some data within a streamholding register 2818 or 2828 is not valid. As described above, such astate can occur at the end of an inner loop when the number of streamelements is less than the respective stream holding register 2818/2828size or at the end of an inner loop when the number of stream elementsremaining is less than the lanes defined by VECLEN. For times not at theend of an inner loop, if VECLEN is less than the width of stream holdingregister 2818/2828 and GRDUP is disabled, then lanes in stream holdingregister 2818/2828 in excess of VECLEN are invalid.

Referring again to FIG. 28, in this example streaming engine 125 furtherincludes valid registers 2819 and 2829. Valid register 2819 indicatesthe valid lanes in stream head register 2818. Valid register 2829indicates the valid lanes in stream head register 2828. Respective validregisters 2819/2829 include one bit for each minimum ELEM_BYTES lanewithin the corresponding stream head register 2818/2828. In thisexample, the minimum ELEM_BYTES is 1 byte. The preferred data path widthof processor 100 and the data length of stream head registers 2818/2828is 64 bytes (512 bits). Valid registers 2819/2829 accordingly have adata width of 64 bits. Each bit in valid registers 2819/2829 indicateswhether a corresponding byte in stream head registers 2818/2828 isvalid. In this example, a 0 indicates the corresponding byte within thestream head register is invalid, and a 1 indicates the correspondingbyte is valid.

In this example, upon reading a respective one of the stream headregisters 2818/2828 and transferring of data to the requestingfunctional unit, the invalid/valid data in the respective valid register2819/2829 is automatically transferred to a data register withinpredicate register file 234 (FIG. 2) corresponding to the particularstream. In this example the valid data for stream 0 is stored inpredicate register P0 and the valid data for stream 1 is stored inpredicate register P1.

The valid data stored in the predicate register file 234 can be used ina variety of ways. The functional unit can combine the vector streamdata with another set of vectors and then store the combined data tomemory using the valid data indications as a mask, thus enabling thesame process to be used for the end of loop data as is used for caseswhere all the lanes are valid which avoids storing invalid data. Thevalid indication stored in predicate register file 234 can be used as amask or an operand in other processes. P unit 246 (FIG. 2) can have aninstruction to count the number of 1's in a predicate register (BITCNT,which can be used to determine the count of valid data elements from apredicate register.

FIG. 32 illustrates example hardware 3200 to produce the valid/invalidindications stored in the valid register 2819 (FIG. 28). FIG. 32illustrates hardware for stream 0; stream 1 includes correspondinghardware. Hardware 3200 operates to generate one valid word each timedata is updated in stream head register 2818 (FIG. 28). A first inputELTYPE is supplied to decoder 3201. Decoder 3201 produces an outputTOTAL ELEMENT SIZE corresponding to the minimum data size based upon theelement size ELEM_BYTES and whether the elements are real numbers orcomplex numbers. The meanings of various codings of ELTYPE are shown inTable 9. Table 27 shows an example output of decoder 3201 in bytes forthe various ELTYPE codings. Note Table 9 lists bits and Table 27 listsbytes. As shown in Table 27, TOTAL ELEMENT SIZE is 1, 2, 4 or 8 bytes ifthe element is real and 2, 4, 8 or 16 bytes if the element is complex.

TABLE 27 Total Element Size ELTYPE Real/Complex Bytes 0000 Real 1 0001Real 2 0010 Real 4 0011 Real 8 0100 Reserved Reserved 0101 ReservedReserved 0110 Reserved Reserved 0110 Reserved Reserved 1000 Complex, NotSwapped 2 1001 Complex, Not Swapped 4 1010 Complex, Not Swapped 8 1011Complex, Not Swapped 16 1100 Complex, Swapped 2 1101 Complex, Swapped 41110 Complex, Swapped 8 1111 Complex, Swapped 16

A second input PROMOTE is supplied to decoder 3202. Decoder 3202produces an output promotion factor corresponding to the PROMOTE input.The meaning of various codings of PROMOTE are shown in Table 28, whichshows an example output of decoder 3202 in bytes for the various PROMOTEcodings. The difference in extension type (zero extension or signextension) is not relevant to decoder 3202.

TABLE 28 Promotion PROMOTE Factor 000 1 001 2 010 4 011 8 100 Reserved101 2 110 4 111 8

The outputs of decoders 3201 and 3202 are supplied to multiplier 3203.The product produced by multiplier 3203 is the lane size correspondingto the TOTAL ELEMENT SIZE and the promotion factor. Because thepromotion factor is an integral power of 2 (2^(N)), the multiplicationcan be achieved by corresponding shifting of the TOTAL ELEMENT SIZE,e.g., no shift for a promotion factor of 1, a one-bit shift for apromotion factor of 2, a two-bit shift for a promotion factor of 4, anda three-bit shift for a promotion factor of 8.

NUMBER OF LANES unit 3204 receives the vector length VECLEN and the LANESIZE and generates the NUMBER OF LANES. Table 29 shows an exampledecoding of the number of lanes for lane size in bytes and the vectorlength VECLEN.

TABLE 29 VECLEN LANE SIZE 000 001 010 011 100 101 110 1 1 2 4 8 16 32 642 — 1 2 4 8 16 32 4 — — 1 2 4 8 16 8 — — — 1 2 4 8 16 — — — — 1 2 4 32 —— — — — 1 2 64 — — — — — — 1

As previously stated, VECLEN must be greater than or equal to theproduct of the element size and the duplication factor. As shown inTable 29, VECLEN must also be greater than or equal to the product ofthe element size and the promotion factor. This means that VECLEN mustbe large enough to guarantee that an element cannot be separated fromits extension produced by type promotion block 2022 (FIG. 20). The cellsbelow the diagonal in Table 29 marked “-” indicate an unpermittedcombination of parameters.

The NUMBER OF LANES output of unit 3204 serves as one input toLANE/REMAINING ELEMENTS CONTROL WORD unit 3211. A second input comesfrom multiplexer 3212. Multiplexer 3212 receives a Loop0 input and aLoop1 input. The Loop0 input and the Loop1 input represent the number ofremaining elements in the current iteration of the corresponding loop.

FIG. 33 illustrates a partial schematic view of address generator 2811shown in FIG. 28. Address generator 2811 forms an address for fetchingthe next element in the defined stream of the corresponding streamingengine. Start address register 3301 stores a start address of the datastream. As previously described above, in this example, start addressregister 3301 is a scalar register in global scalar register file 211designated by the SEOPEN instruction that opened the correspondingstream. The start address can be copied from the specified scalarregister and stored locally at the respective address generator2811/2821 by control logic included with address generator 2811. Thefirst loop of the stream employs Loop0 count register 3311, adder 3312,multiplier 3313 and comparator 3314. Loop0 count register 3311 storesthe working copy of the iteration count of the first loop (Loop0). Foreach iteration of Loop0, adder 3312, as triggered by the Next Addresssignal, adds 1 to the loop count, which is stored back in Loop0 countregister 3311. Multiplier 3313 multiplies the current loop count and thequantity ELEM_BYTES. ELEM_BYTES is the size of each data element inloop0 in bytes. Loop0 traverses data elements physically contiguous inmemory with an iteration step size of ELEM_BYTES.

Comparator 3314 compares the count stored in Loop0 count register 3311(after incrementing by adder 3313) with the value of ICNT0 2901 (FIG.29) from the corresponding stream template register 2900 (FIG. 29). Whenthe output of adder 3312 equals the value of ICNT0 2901 of the streamtemplate register 2900, an iteration of Loop0 is complete. Comparator3314 generates an active Loop0 End signal. Loop0 count register 3311 isreset to 0 and an iteration of the next higher loop, in this case Loop1,is triggered.

Circuits for the higher loops (Loop1, Loop2, Loop3, Loop4 and Loop5) aresimilar to that illustrated in FIG. 33. Each loop includes a respectiveworking loop count register, adder, multiplier and comparator. The adderof each loop is triggered by the loop end signal of the prior loop. Thesecond input to each multiplier is the corresponding dimension DIM1,DIM2, DIM3, DIM4 and DIM5 from the corresponding stream template. Thecomparator of each loop compares the working loop register count withthe corresponding iteration value ICNT1, ICNT2, ICNT3, ICNT4 and ICNT5of the corresponding stream template register 2900. A loop end signalgenerates an iteration of the next higher loop. A loop end signal fromLoop5 ends the stream.

FIG. 33 also illustrates the generation of Loop0 count. Loop0 countequals the updated data stored in the corresponding working countregister 3311. Loop0 count is updated on each change of working Loop0count register 3311. The loop counts for the higher loops (Loop1, Loop2,Loop3, Loop4 and Loop5) are similarly generated.

FIG. 33 also illustrates the generation of Loop0 address. Loop0 addressequals the data output from multiplier 3313. Loop0 address is updated oneach change of working Loop0 count register 3311. Similar circuits forLoop1, Loop2, Loop3, Loop4 and Loop5 produce corresponding loopaddresses. In this example, Loop0 count register 3311 and the other loopcount registers are implemented as count up registers. In anotherexample, initialization and comparisons operate as count down circuits.

Referring again to FIG. 32, the value of the loop down count, such asLoop0/, is given by expression (2).Loopx/=ICNTx−Loopx  (2)That is, the loop down count is the difference between the initialiteration count specified in the stream template register and the loopup count produced as illustrated in FIG. 33.

LANE/REMAINING ELEMENTS CONTROL WORD unit 3211 (FIG. 32) generates acontrol word 3213 based upon the number of lanes from NUMBER OF LANESunit 3204 and the loop down count selected by multiplexer 3212. Thecontrol input to multiplexer 3212 is the TRANSPOSE signal from field3002 of FIG. 30. If TRANSPOSE is disabled (“000”), multiplexer 3212selects the Loop0 down count Loop0. For all other legal values ofTRANSPOSE (“001”, “010”, “011”, “100”, “101” and “110”) multiplexer 3212selects the Loop1 down count Loop1/. The streaming engine maps theinnermost dimension to consecutive lanes in a vector. For normal streamsthis is Loop0. For transposed streams, this is Loop1, becausetransposition exchanges the two dimensions.

LANE/REMAINING ELEMENTS CONTROL WORD unit 3211 generates control word3213 as follows. Control word 3213 has a number of bits equal to thenumber of lanes from unit 3204. If the remaining count of elements ofthe selected loop is greater than or equal to the number of lanes, thenall lanes are valid. For this case, control word 3213 is all ones,indicating that all lanes within the vector length VECLEN are valid. Ifthe remaining count of elements of the selected loop is nonzero and lessthan the number of lanes, then some lanes are valid and some areinvalid. According to the lane allocation described above in conjunctionwith FIGS. 21 and 22, stream elements are allocated lanes starting withthe least significant lanes. Under these circumstances, control word3213 includes a number of least significant bits set to one equal to thenumber of the selected loop down count. All other bits of control word3213 are set to zero. In the example illustrated in FIG. 32, the numberof lanes equals eight and there are five valid (1) least significantbits followed by three invalid (0) most significant bits whichcorresponds to a loop having five elements remaining in the finaliteration.

Control word expansion unit 3214 expands the control word 3213 basedupon the magnitude of LANE SIZE. The expanded control word includes onebit for each minimally sized lane. In this example, the minimum streamelement size, and thus the minimum lane size, is one byte (8 bits). Inthis example, the size of holding registers 2818/2828 equals the vectorsize of 64 bytes (512 bits). Thus, the expanded control word has 64bits, one bit for each byte of stream holding registers 2818/2828. Thisexpanded control word fills the least significant bits of thecorresponding valid register 2819 and 2829 (FIG. 28).

For the case when VECLEN equals the vector length, the description iscomplete. The expanded control word includes bits for all places withinrespective valid register 2819/2829. There are some additionalconsiderations when VECLEN does not equal the vector length. When VECLENdoes not equal the vector length, the expanded control word does nothave enough bits to fill the corresponding valid register 2819/2829. Asillustrated in FIG. 32, the expanded control word fills the leastsignificant bits of the corresponding valid register 2819/2829, thusproviding the valid/invalid bits for lanes within the VECLEN width.Another mechanism is provided for lanes beyond the VECLEN width up tothe data width of stream head register 2818.

Referring still to FIG. 32, multiplexer 3215 and group duplicate unit3216 are illustrated to provide the needed additional valid/invalidbits. Referring to the description of VECLEN, if group duplication isnot enabled (GRDUP=0), then the excess lanes are not valid. A firstinput of multiplexer 3215 is an INVALID 0 signal that includes multiplebits equal in number to VECLEN. When GRDUP=0, multiplexer 3215 selectsthis input. Group duplicate unit 3216 duplicates this input to allexcess lanes of stream head register 2818. Thus, the most significantbits of valid register 2819 are set to zero indicating the correspondingbytes of stream head register 2818 are invalid. This occurs for vectors1-8 of the example shown in Table 15, vectors 1-15 of the example shownin Table 16, and vectors 1-29 of the example shown in Table 17.

In another example, mux 3215 and group duplicate block 3216 are replacedwith group duplicate logic that is similar to the group duplicate logic2025 illustrated in FIG. 31.

As previously described, if group duplication is enabled (GRDUP=1), thenthe excess lanes of stream head register 2818 (FIG. 28) are filled withcopies of the least significant bits. A second input of multiplexer 3215is the expanded control word from control word expansion unit 3214. WhenGRDUP=1, multiplexer 3215 selects this input. Group duplicate unit 3216duplicates this input to all excess lanes of stream head register 2818.

There are two possible outcomes. In one outcome, in most cases, all thelanes within VECLEN are valid and the bits from control word expansionunit 3214 are all ones. This occurs for vectors 1-7 of the groupduplication example shown in Table 18 and vectors 1-14 of the groupduplication example shown in Table 19. Under these conditions, all bitsof the expanded control word from control word expansion unit 3214 areone and all lanes of stream head register 2818 are valid. Groupduplicate unit 3216 thus fills all the excess lanes with ones. In theother outcome, the number of remaining stream data elements is less thanthe number of lanes within VECLEN. This occurs for vector 8 in the groupduplication example shown in Table 18 and vector 15 in the groupduplication example shown in Table 19. Under these conditions, somelanes within VECLEN are valid and some are invalid. Group duplicate unit3216 fills the excess lanes with bits having the same pattern as theexpanded control word bits. In either case, the excess lanes are filledcorresponding to the expanded control bits.

Referring still to FIG. 32, a boundary 3217 is illustrated between theleast significant bits and the most significant bits. The location ofthis boundary is set by the size of VECLEN relative to the size ofstream head register 2818.

FIG. 34 is a partial schematic diagram 3400 illustrating the streaminput operand coding described above. FIG. 34 illustrates a portion ofinstruction decoder 113 (see FIG. 1) decoding src1 field 1305 of oneinstruction to control corresponding src1 input of functional unit 3420.These same or similar circuits are duplicated for src2/cst field 1304 ofan instruction controlling functional unit 3420. In addition, thesecircuits are duplicated for each instruction within an execute packetcapable of employing stream data as an operand that are dispatchedsimultaneously.

Instruction decoder 113 receives bits 13-17 of src1 field 1305 of aninstruction. The opcode field (bits 3-12 for all instructions andadditionally bits 28-31 for unconditional instructions) unambiguouslyspecifies a corresponding functional unit 3420 and the function to beperformed. In this example, functional unit 3420 can be L2 unit 241, S2unit 242, M2 unit 243, N2 unit 244 or C unit 245. The relevant part ofinstruction decoder 113 illustrated in FIG. 34 decodes src1 bit field1305. Sub-decoder 3411 determines whether src1 bit field 1305 is in therange from 00000 to 01111. If this is the case, sub-decoder 3411supplies a corresponding register number to global vector register file231. In this example, the register number is the four least significantbits of src1 bit field 1305. Global vector register file 231 recallsdata stored in the register corresponding to the register number andsupplies the data to the src1 input of functional unit 3420.

Sub-decoder 3412 determines whether src1 bit field 1305 is in the rangefrom 10000 to 10111. If this is the case, sub-decoder 3412 supplies acorresponding register number to the corresponding local vector registerfile. If the instruction is directed to L2 unit 241 or S2 unit 242, thecorresponding local vector register file is local vector register file232. If the instruction is directed to M2 unit 243, N2 unit 244 or Cunit 245, the corresponding local vector register file is local vectorregister file 233. In this example, the register number is the threeleast significant bits of src1 bit field 1305. The corresponding localvector register file 232/233 recalls data stored in the registercorresponding to the register number and supplies the data to the src1input of functional unit 3420.

Sub-decoder 3413 determines whether src1 bit field 1305 is 11100. Ifthis is the case, sub-decoder 3413 supplies a stream 0 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 0 datastored in holding register 2818 to the src1 input of functional unit3420.

Sub-decoder 3414 determines whether src1 bit field 1305 is 11101. Ifthis is the case, sub-decoder 3414 supplies a stream 0 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 0 datastored in holding register 2818 to the src1 input of functional unit3420. Sub-decoder 3414 also supplies an advance signal to stream 0. Aspreviously described, streaming engine 125 advances to store the nextsequential vector of data elements of stream 0 in holding register 2818.

Supply of a stream 0 read signal to streaming engine 125 by eithersub-decoder 3413 or sub-decoder 3414 triggers another data movement.Upon such a stream 0 read signal, streaming engine 125 supplies the datastored in valid register 2819 to predicate register file 234 forstorage. In accordance with this example, this is a predetermined dataregister within predicate register file 234. In this example, dataregister P0 corresponds to stream 0.

Sub-decoder 3415 determines whether src1 bit field 1305 is 11110. Ifthis is the case, sub-decoder 3415 supplies a stream 1 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 1 datastored in holding register 2828 to the src1 input of functional unit3420.

Sub-decoder 3416 determines whether src1 bit field 1305 is 11111. Ifthis is the case, sub-decoder 3416 supplies a stream 1 read signal tostreaming engine 125. Streaming engine 125 then supplies stream 1 datastored in holding register 2828 to the src1 input of functional unit3420. Sub-decoder 3414 also supplies an advance signal to stream 1. Aspreviously described, streaming engine 125 advances to store the nextsequential vector of data elements of stream 1 in holding register 2828.

Supply of a stream 1 read signal to streaming engine 125 by eithersub-decoder 3415 or sub-decoder 3416 triggers another data movement.Upon such a stream 1 read signal, streaming engine 125 supplies the datastored in valid register 2829 to predicate register file 234 forstorage. In accordance with this example, this is a predetermined dataregister within predicate register file 234. In this example, dataregister P1 corresponds to stream 1.

Similar circuits are used to select data supplied to scr2 input offunctional unit 3402 in response to the bit coding of src2/cst field1304. The src2 input of functional unit 3420 can be supplied with aconstant input in a manner described above. If instruction decoder 113generates a read signal for stream 0 from either scr1 field 1305 orscr2/cst field 1304, streaming engine 125 supplies the data stored invalid register 2819 to predicate register P0 of predicate register file234 for storage. If instruction decode 113 generates a read signal forstream 1 from either scr1 field 1305 or scr2/cst field 1304, streamingengine 125 supplies the data stored in valid register 2829 to predicateregister P1 of predicate register file 234 for storage.

The exact number of instruction bits devoted to operand specificationand the number of data registers and streams are design choices. Inparticular, the specification of a single global vector register fileand omission of local vector register files is feasible. This exampleemploys a bit coding of an input operand selection field to designate astream read and another bit coding to designate a stream read andadvancing the stream.

The process illustrated in FIG. 34 automatically transfers valid datainto predicate register file 234 each time stream data is read. Thetransferred valid data can then be used by P unit 246 for furthercalculation of meta data. The transferred valid data can also be used asa mask or as an operand for other operations by one or more of vectordata path side B 116 functional units including L2 unit 241, S2 unit242, M2 unit 243, N2 unit 244 and C unit 245. There are numerousfeasible compound logic operations employing this stream valid data.

FIG. 35 is a partial schematic diagram 3500 illustrating another exampleconfiguration for selecting operand sources. In this example, therespective stream valid register 2819/2829 need not be automaticallyloaded to a predetermined register in predicate register file 234.Instead, an explicit instruction to P unit 246 is used to move the data.FIG. 35 illustrates a portion of instruction decoder 113 (see FIG. 1)decoding src1 field 1305 of one instruction to control a correspondingsrc1 input of P unit 246. These same or similar circuits can beduplicated for src2/cst field 1304 (FIG. 13) of an instructioncontrolling P unit 246.

Instruction decoder 113 receives bits 13-17 of src1 field 1305 of aninstruction. The opcode field opcode field (bits 3-12 for allinstructions and additionally bits 28-31 for unconditional instructions)unambiguously specifies P unit 246 and the function to be performed. Therelevant part of instruction decoder 113 illustrated in FIG. 35 decodessrc1 bit field 1305. Sub-decoder 3511 determines whether src1 bit field1305 is in the range 00000 to 01111. If this is the case, sub-decoder3511 supplies a corresponding register number to global vector registerfile 231. In this example, the register number is the four leastsignificant bits of src1 bit field 1305. Global vector register file 231recalls data stored in the register corresponding to the register numberand supplies the data to the src1 input of P unit 246.

Sub-decoder 3512 determines whether src1 bit field 1305 is in the range10000 to 10111. If this is the case, sub-decoder 3512 supplies a decodedregister number to the predicate register file 234. In this example, theregister number is the three least significant bits of src1 bit field1305. The predicate register file 234 recalls data stored in theregister corresponding to the register number and supplies the data tothe src1 input of predicate unit 246.

Sub-decoder 3513 determines whether src1 bit field 1305 is 11100. Ifthis is the case, sub-decoder 3513 supplies a stream 0 valid read signalto streaming engine 125. Streaming engine 125 then supplies valid datastored in valid register 2819 to the src1 input of P unit 246.

Sub-decoder 3514 determines whether src1 bit field 1305 is 11101. Ifthis is the case, sub-decoder 3514 supplies a stream 1 valid read signalto streaming engine 125. Streaming engine 125 then supplies stream 1valid data stored in valid register 2829 to the src1 input of P unit246.

The P unit 246 instruction employing the stream valid register 2819/2829as an operand can be any P unit instruction previously described such asNEG, BITCNT, RMBD, DECIMATE, EXPAND, AND, NAND, OR, NOR, and XOR.

The special instructions noted above can be limited to P unit 242. Thus,the operations outlined in FIGS. 34 and 35 can be used together. If thefunctional unit specified by the instruction is L2 unit 241, S2 unit242, M2 unit 243, N2 unit 244 or C unit 245, then src1 field 1305 isinterpreted as outlined with respect to FIG. 34. If the functional unitspecified by the instruction is P unit 246, then src1 field 1305 isinterpreted as outlined with respect to FIG. 35. Alternatively, theautomatic saving of the stream valid register to a predeterminedpredicate register illustrated in FIG. 34 can be implemented in oneexample and not implemented in another example.

Matrix Multiplication Accelerator

FIG. 36 is a block diagram of a system 3600 that includes processingunit core 110, streaming engine 125, system memory 3630, and matrixmultiplication accelerator (MMA) 3640. MMA 3640 is a tightly coupledmatrix multiplication acceleration unit that is a third type of functionunit for processing unit core 110. The other two are the traditionalscalar data path 115 (FIG. 1) and the vector data path 116 (FIG. 1). MMA3640 enables system 3600 to fulfill a large group of image and dataprocessing application requirements. MMA 3640 supports highcomputational performance requirements in matrix multiplications. Withsupport from streaming engine 125, processing unit core 110, and L2memory 130, MMA 3640 efficiently computes large numbers of MACs(multiple accumulation) required by various vision algorithms, denselinear algebra, FFT operations and high level apps includingconvolutional neural networks (CNNs), structure from motion (SFM),Radar, etc. without increasing the memory bandwidth into the processingunit core 110.

Generally speaking, MMA 3640 supports matrix multiplication of twomatrices. As shown in expression (3), where matrix A is an [n×m] matrixand matrix B is an [m×p] matrix, the matrix multiplication outputsmatrix C.C _(ij)=Σ_(k=1) ^(m) A _(ik) *B _(kj)  (3)where each i,j entry is given by multiplying the entry Aik (across row iof A) by the entries Bkj (down column j of B), for k=1, 2, . . . , m.

FIG. 37 illustrates an example matrix A, matrix B and a resulting matrixC in more detail. Each result element C_(ij) is a summation of productsof elements from a row of matrix A and a column of matrix B as definedby expression (3).

Referring back to FIG. 36, MMA includes an A[.] buffer 3641 to hold amatrix A, a B[.] buffer 3642 to hold a matrix B, and a C[.] buffer 3643to collect the result elements for matrix C. MMA 3643 includes an arrayof individual multipliers and a set of accumulators as indicated at 3644to allow an entire row of the C matrix to be calculated in one executioncycle of MMA 3640. In an example, MMA 3640 is equipped to handle a 32×3216-bit fixed/floating point matrix multiply and to produce a 32×3216-bit product matrix in 32 cycles.

In an example, MMA 3640 is also equipped to multiply two 64×64 8-bitmatrices by breaking each into four 32×32 sub-matrices, multiplyingvarious combinations of the sub-matrices and then combining the resultsto produce a final 64×64 8-bit matrix result. Other examples may beimplemented to support larger or smaller matrices having a larger orsmaller precision than 8 or 16-bits.

In order for MMA 3640 to operate correctly on a matrix that is smallerthan its native size, such as the 32×32 example mentioned above, all ofthe elements of each input matrix A and B should contain valid data.Unused elements should be set to zero, or some other agreed upon nullvalue. Streaming engine 125 includes support for nulling unused elementsof an array during a stream access without performing additional memoryaccesses, as described in more detail hereinbelow. In an example,streaming engine 125 includes support for inserting zeros or a selectedvalue, such as a max value or a min value, during a stream accesswithout performing memory accesses to provide the selected values.

Streaming Engine Support for MMA

Referring still to FIG. 36, streaming engine 125 interfaces with L2memory 130 via unified memory controller (UMC) 3601. UMC 3601coordinates access to L2 memory 130 by the various functional units insystem 3600. Data routing unit 3602 interfaces with UMC 3601 to routedate into the system memory 130. The outputs of stream head registers2818/2828 (FIG. 28) and valid registers 2819/2829 (FIG. 28) are providedto streaming engine interface 3611 and thence to logical units inprocessing unit core 110 via respective buses 2840/2841. In thisexample, S unit 242 can be programmed to pass one stream from SE 125 toMMA A[.] buffer 3641 and to pass the other stream from SE 125 to B[.]buffer 3642. The output of product matrix C[.] may be directed to L2memory 130 via UMC 3601, or to a destination register in register file233 via a destination multiplexer shown in C unit 245.

FIG. 38 is a more detailed block diagram of a portion of the streamingengine 125 of FIG. 28. Linear streams work for large classes ofalgorithms, but not all. For example, matrix multiplication presents aunique problem for the streaming engine in that each element in thematrix product contains the result of a vector dot product between a rowfrom the first matrix and a column from the second matrix. Programstypically store matrices all in row-major or column-major order.Row-major order stores all the elements of a single row contiguously inmemory. C and C++ programs typically store arrays in row-major order.Column-major order stores all elements of a single column contiguouslyin memory. FORTRAN programs typically stores arrays in column-majororder. Depending on the programming language, matrices typically getstored in the same order as the default array order for the language.

As a result, only one of the two matrices in a matrix multiplication mapon to the streaming engine's 2-dimensional stream definition. Thisproblem is not unique to the streaming engine. In fact, matrixmultiplication's access pattern fits poorly with most general-purposememory hierarchies. Some software libraries attack this problem bydirectly transposing one of the two matrices, so that both get accessedrow-wise (or column-wise) during multiplication.

Transpose Mode

With the streaming engine, programs need not resort to that extreme. Thestreaming engine supports implicit matrix transposition with a notion oftransposed streams. Transposed streams avoid the cost of explicitlytransforming the data in memory. Instead of accessing data in strictlyconsecutive-element order, the streaming engine effectively interchangesthe inner two loop dimensions in its traversal order, fetching elementsalong the second dimension into contiguous vector lanes.

Transpose mode interchanges the two innermost loop levels. That is, intranspose mode, the two innermost loops ICNT0 and ICNT1 areinterchanged. ICNT1 determines the number of rows in each column. Acolumn is defined as a GRANULE size. ICNT0 is the second dimension in atranspose stream and defines the horizontal width (which may or may notbe a multiple of the GRANULE). In this example streaming engine, themaximum row height, ICNT1, must be at least 1 and less than or equal 16.There are no restrictions on the ICNT0 in transpose. However, if theICNT0 is not a multiple of the GRANULE size, the streaming engine willpad zeros in the missing elements of each GRANULE.

Coarse rotator 2835 and data storage 2816 of stream 0 engine 2810 areillustrated in FIG. 38; however, coarse rotator 2836 and data storage2826 of stream 1 engine 2820 are similar and operate in a similarmanner. Transpose mode is performed by stream 0 engine 2810 (FIG. 28)using resources of coarse rotator 2835, data storage unit 2816, andbutterfly network 2817. Transpose mode is performed by stream 1 engine2820 (FIG. 28) using resources of coarse rotator 2836 (FIG. 28), datastorage unit 2826 (FIG. 28), and butterfly network 2827 (FIG. 28).

In this example, data storage 2816 is organized as a register file 3810with 32 slots of 64 bytes (512 bits). Other examples may provide alarger or a smaller amount of storage without changing the semantics ofa stream. Data storage 2816 is organized as eight independent banks thatare each eight bytes (64 bits) wide. Each bank includes two write portsand two read ports. In this example, each bank also includes twobits/line for parity protection.

In Transpose mode, the SE organizes the internal storage into sectortiles, and the number of sector tiles depends on what the currentvertical count (ICNT1) is set to. This allows the SE to fetch as manyrows and columns as possible and organizes and rotates the data comingback from L2 into the sectors. This allows the SE to use both read andwrite ports per bank when reading and writing the data in transposemode, so that the data can be rotated and ordered according to itssector.

In this example, coarse rotator 2835 includes a set of sixteenmultiplexors, represented by multiplexors 3806, 3807, 3808. Eachmultiplexor, such as multiplexor 3806, has sixteen inputs that are eachfour bytes (32 bits) wide and are connected to receive all 512 bitsprovided by the L2 interface 2833 on bus 3802. A four-byte output ofeach multiplexor is coupled to provide data to one half of a respectivebank of register file 3810. Each bank of register file 3810 is coupledto receive data from two multiplexors in parallel, such as 3806, 3807,such that data received from the L2 interface via bus 3802 may bemanipulated in four-byte elements.

Reference queue 2815 receives storage allocation and tracking meta-datafrom storage and allocation logic 2814 (FIG. 28). As each 512-bit lineof data is received from L2 via L2 interface 2833 (FIG. 28), controllogic 3804 generates control signals to independently control each ofthe sixteen multiplexors 3806, 3807, 3808 such that any four-byte dataelement from the received 512-bit line of data may be stored in eitherside of each of the eight banks in a selected slot of register file 3810based on the meta-data provided by reference queue 2815. Coarse rotator2835 allows each 512-bit line of data to be rotated, shifted, truncated,or duplicated by stream 0 engine 2810 as discussed in more detail above.Furthermore, matrix transposition may be performed by stream 0 engine2810 using the coarse rotator 2835, as will be described in more detailbelow.

Alignment network 3820 and 3821 are each similar to coarse rotator 2835.In this example, alignment network 3820 includes a set of sixteenmultiplexors, represented by multiplexors 3822, 3823. Each multiplexor,such as multiplexor 3822, has thirty-two inputs that are each four bytes(32 bits) wide and are connected to receive all 512 bits provided byeach of the two read ports of the register file 3810. A four-byte outputof each multiplexor, such as multiplexor 3822, is coupled to providedata to a respective input of butterfly network 2817. In this manner,multiplexors 3822, 3823 can select sixteen four-byte data elements fromregister file 3810 to form a 64-byte line of data to provide tobutterfly network 2817.

Similarly, in this example, alignment network 3821 includes a set ofsixteen multiplexors, represented by multiplexors 3824, 3825. Eachmultiplexor, such as multiplexor 3824, has thirty-two inputs that areeach four bytes (32 bits) wide and are connected to receive all 512 bitsprovided by each of the two read ports of the register file 3810. Afour-byte output of each multiplexor, such as multiplexor 3824, iscoupled to provide data to a respective input of butterfly network 2817.In this manner, multiplexors 3824, 3825 can select sixteen four-bytedata elements from register file 3810 to form a 64-byte line of data toprovide to butterfly network 2817.

Control logic 3814 generates control signals to independently controleach of the sixteen multiplexors 3822, 3823 in alignment network 3820and each of the sixteen multiplexors 3824, 3825 in alignment network3821 such that any four-byte data element retrieved from register file3810 may be aligned to any four-byte location within two 64-byte outputlines provided to butterfly network 2817 based on the meta-data providedby reference queue 2815.

Butterfly network 2817 is controlled by stream 0 engine 2810 to furtherformat data retrieved from data storage 2816 prior to sending theformatted data to processing unit core 110, as described in more detailwith regard to FIG. 20, FIG. 28. Butterfly network 2817 includesmultiple ranks of cross-coupled multiplexor nodes to perform the dataformatting.

In this example, control logic 3804 for coarse rotator 2835 and controllogic 3814 for data storage 2816 are implemented as asynchronous Booleanlogic that is capable of generating control signals for each of themultiplexors and register file 3810 in parallel based on the contents ofthe meta-data provided by reference queue 2815.

In Transpose mode, SE0 2810 organizes the internal storage 2816 intosector tiles, and the number of sector tiles depends on what the currentvertical count (ICNT1) is set too. This allows the SE0 2810 to fetch asmany rows and columns as possible and organizes and rotates the datacoming back from L2 130 (FIG. 1) into the sectors of data storage 2816.In this example, the register file 3810 includes 32 rows×64 bytes and isorganized as eight independent 4-port banks. This allows SE0 2810 to useboth read/write ports per bank when reading and writing the data intranspose mode, since the data is rotated and ordered according to itssector.

The coarse rotator is controlled by control logic 3804 based onmeta-data that is queued up in reference queue 2815 (FIG. 28, FIG. 38).The meta-data is derived from the stream parameters for matrix 3700 bystorage allocation tracking logic 2814 (FIG. 28).

Inserting Null Vectors into a Stream

Referring to FIG. 38, control logic 3814 can control each of themultiplexers on alignment networks 3820, 3821 to force a null value ontoselected elements of a stream vector based on the meta-data provided byreference queue 2815. In this manner, an entire stream vector can be setto a null value without fetching any data from system memory. In anexample, the null value is “0.” In another example, a predefined valueor pattern may be used to represent a null value.

In another example, control logic 3814 can control each of themultiplexers on alignment networks 3820, 3821 to force a selected valueonto selected elements of a stream vector based on the meta-dataprovided by reference queue 2815. In this manner, an entire streamvector can be set to a selected value, such as a min value or a maxvalue without fetching any data from system memory.

In this example, control logic in the address generator 2811/2821 (seeFIG. 28) performs count tracking for the six levels of nestediterations. As will be described in more detail hereinbelow, variousconditions may be detected that are associated with one or more of thesix levels of nested iterations and used to signal that a null value ora selected value is to be inserted into the vector stream withoutfetching data from memory for the null value or selected value vector.

Metadata produced by the address generator is pushed into the streamreference queue 2815/2825 (see FIG. 28). On the backend, when processingunit core 110 (FIG. 1) performs a read, this metadata is popped out andsent to control logic 3814 in alignment network 2820/2821 with the lanesto be nulled or set to a selected value without reading data from systemmemory. The metadata keeps track of decrement dimensions (DECDIM) anddimension widths (DECDIM_WIDTH) and is fed to backend logic, asdescribed hereinbelow in more detail.

Data Strip Mining Support

Complex signal processing applications such as various visionalgorithms, dense linear algebra, FFT operations and high-level appsincluding convolutional neural networks (CNNs), structure from motion(SFM), and Radar may require numeric manipulation of a complexmultidimensional data structure. Boundaries of the data structure needto be clean so that anomalous data is not included in computations doneat the boundary. Generally, this requires a programmer to allocatememory space at the boundary of a data structure that can be preset to aknown value, such as zero, or a maximum or minimum data value.Presetting the boundary data then takes additional processing cycles toaccess and set the boundary data values.

An example steaming engine 125 (FIG. 1) includes a feature to allow aprogrammer to specify a decrement dimension (DECDIM_WIDTH) parameter forone or more of the six-dimensional nested loops supported by steamingengine 125 that is different from a dimension defined by a respectiveloop dimension parameter. In this manner, streaming engine 125 can beprogrammed to insert the appropriate known value into the data stream asthe data stream is being fetched from system memory by the streamingengine. Furthermore, streaming engine 125 can be programmed to insertnull or known value stream vectors that correspond to boundary area ofthe data structure without accessing the system memory for theseboundary area stream vectors, thereby reducing processing cycles andtime.

In an example, the DECDIM feature uses two sets of flags that includes afirst decrement flag (DECDIMx), where “x” is “1” or “2” in this example,a secondary decrement flag (DECDIMxSD), and a respective width parameter(DECDIMx_WIDTH). This allows a programmer to define four mask values onselected dimensions of the nested loops in order to mask or zero outparts of the stream data. Table 30 defines an example set of DECDIMflags that apply to an example of streaming engine 125. In this example,three bits are used to define the DECDIMx flag, while only two bits areused to define the DECDIMxSD flag. The DECDIMxSD flag is thereforelimited to DIM1-DIM3 in this example. Various combinations of settingsfor DECDIM are supported, as described in more detail hereinbelow.

TABLE 30 DECDIM flags to control data strip mining operation DECDIMMeaning 000b Normal operating mode DECDIM_WIDTH count is decremented byDIM1 value when entering DIM1. Reloaded when DIM1, or higher DIMs expire010b DECDIM_WIDTH count is decremented by DIM2 value when entering DIM2.Reloaded when DIM2, or higher DIMs expire. 011b DECDIM_WIDTH count isdecremented by DIM3 value when entering DIM3. Reloaded when DIM3, orhigher DIMs expire. 100b DECDIM_WIDTH count is decremented by DIM4 valuewhen entering DIM4. Reloaded when DIM4, or higher DIMs expire. 101bDECDIM_WIDTH count is decremented by DIM5 value when entering DIM5.Reloaded when DIM5 expires (end of stream). 110b, 111b Reserved

Referring to FIG. 29, two DECDIMx_WIDTH fields 2931, 2932 are definedwithin stream template register 2900. DECDIM1_WIDTH 2931 is used inconjunction with DECDIM1 flag 3019 (FIG. 30) and DECDIM1SD flag 3020(FIG. 30) that are included in the flag field 2921 of stream templateregister 2900. DECDIM2_WIDTH 2932 is used in conjunction with DECDIM2flag 3019 (FIG. 30) and DECDIM2SD flag 3020 (FIG. 30).

The DECDIMx flag field and DECDIMx_WIDTH supports a data strip miningfeature that allows a programmer to define a “total actual width” sizeof an image using the DECDIM_WIDTH count to provide this maximum actualwidth. In this mode, the DECDIM_WIDTH is decremented by the selecteddimension (DIM1-DIM5), as shown in Table 30, when the address generator2811/2821 (FIG. 28) enters that loop dimension. For example, ifDECDIM=010b, then every time the loop enters dimension 2, the currentvalue of DECDIM_WIDTH is decremented by the DIM2 value. When theDECDIM_WIDTH becomes less than the ICNT0 (the “Tile Width” in DECDIMmode), the SE 125 will pad the unused elements with zero data. This isreferred to as “data strip mining”.

The DECDIM_WIDTH count value will only reload to the programmed valueagain when the selected DECDIM dimension loop count (ICNT) expires. Inthe above example, the width would reload when dimension 2 (i.e., ICNT2)expires, and dimension 3 is entered. In other words, the width reloadswhen we enter any dimension higher than the selected DECDIM dimension.Thus, it is possible to program the width smaller than the loopiterations count for the selected dimension, which could cause the widthcount to underflow. This is explained further hereinbelow.

As mentioned above, there is also a secondary DECDIMxSD flag. Thesecondary flag allows a “secondary decrement” count mask on top of itsrespective DECDIMx flag for the respective DECDIM_WIDTH. In other words,the respective DECDIM_WIDTH is decremented or reloaded using thesettings for both of the respective DECDIMx and DECDIMxSD when therespective selected dimension is entered or ends.

In an example, the DECDIM selection can be set for any DIM1-DIM5 whileoperating in linear mode. However, in transpose mode, DIM1 selection isnot supported and only DIM2-DIM5 is supported. In this example, theselected DIMx value must be an unsigned value (i.e., DIMx bit 31 iszero). All other dimensions can be unsigned or signed.

For example, if DECDIM=010b, then DIM2 must be an unsigned value. DIM1,DIM3, DIM4, and DIM5 can be unsigned or signed. In example hardware, theinnermost loop count is scaled in terms of total number of bytes. Inother words, the innermost loop ICNT value is equal to(ICNT0×ELEM_BYTES), and in the case of DECDIM mode, the DECDIM_WIDTHcount is (DECDIM_WIDTH×ELEM_BYTES). During processing unit core 110fetches, the innermost loop count expires when all elements have beenconsumed before accounting for any data formatting (element duplication,promotion, decimation). Thus, with data formatting enabled, multipleprocessing unit core 110 fetches could occur before the innermost loopcount expires.

In an example, the value of DECDIM_WIDTH count will be saturated at zeroin the case where the loop iteration count parameters for the selectedDECDIM (i.e., ICNT1-ICNT5) are incorrectly programmed causingDECDIM_WIDTH count to underflow when decremented with the selected DIMxvalue. When saturation occurs, streaming engine 125 will holdDECDIM_WIDTH count at zero and subsequent data phases to processing unitcore 110 will also be zero.

The following tables and FIGS. 39-42 illustrate various examples howthis feature operates. FIG. 39 illustrates what a “normal” streampattern would look like. FIGS. 40-42 illustrate several examples of whatdata strip mining patterns would look like. The DECDIM_WIDTH value inthe tables represent the count of the entire frame, which getsdecremented by the selected DIMx value as each DECDIM dimension isentered. Note that the examples show data moving left to right, thus theLSByte is leftmost. Also, the FIGS. 39-42 do not enable any ‘dataformatting’. If data formatting is enabled, additional processing unitcore 110 fetches would be required to consume each of the “Tile” width,i.e., innermost ICNT0.

SE 125 will not send any tTLB 2812/2822 (FIG. 28) or L2 130 (FIG. 1)fetches for regions which have been fully masked and zeroed out(DECDIM_WIDTH saturated), and thus programmers need not allocate theseregions in memory even though the stream addressing patterns cover theseregions. SE 125 does this by keeping track of the overall DECDIM_WIDTHmask count and applying the DECDIMx and DECDIMxSD settings, and whenthis count saturates to zero or ends on a 64-byte line boundary, allsubsequent L2 fetches are blocked. By doing this, SE 125 suppresses anyerrors or faults associated with subsequent un-allocated regions sinceno TLB 2812/2822 or L2 130 fetches are sent.

Transpose data strip mining is similar to linear data strip miningexcept the data moves in a transpose pattern. DECDIM flags provides thedimension for when the DECDIM_WIDTH count decrement occurs. This allowsthe data strip mask to apply to the remaining elements in the GRANULE.In DECDIM mode and transpose, the setting for DECDIM=DIM1 is notsupported as mentioned in previous tables. Note that for normaltranspose patterns, when the ICNT0 is not a multiple of the GRANULE,gappy data occurs and is filled with zeros. Similarly, gappy data occursin DECDIM transpose mode when the ICNT0 is not a multiple of theGRANULE, in addition to the data strip masking that is applied usingDECDIM_WIDTH.

FIGS. 39, 40, 41, 42, and 43 illustrate several example linear streamtransfers that can be performed by example streaming engine 125. Theseexamples are by no means an exhaustive list of the variousconfigurations of stream transfers the can be performed by thesix-dimensional nested loop control logic included within streamingengine 125.

FIG. 39 illustrates an example of a normal mode stream transfer 3900 inwhich the DECDIM flags are set to “000b” as shown in Table 30. Table 31lists the stream parameters that are placed in the stream templateregister 2900 (FIG. 29). In this example, VECLEN=16 elements, and eachelement is one byte. Therefore, each stream vector includes 16 bytes ofarray elements data. The inner loop specified by ICNT0=56 bytes,therefore streaming engine 125 will make fetches to system memory 130(FIG. 1) until 56 bytes of array data have been retrieved. In this case,fetch 1 indicated at 3921 actually retrieves 64 bytes of data fromsystem memory 130, but only 16 bytes of data beginning at address 0x0are used to form the first stream vector. The rest of the vectorprovided to processing unit core 110 (FIG. 1) is zero filled byalignment network 3820/3821 (FIG. 39) as described hereinabove.Similarly, fetch 2 3922, fetch 3 3923 and fetch 4 3924 access systemmemory 130 to form three additional stream vectors to provide toprocessing unit core 110. However, ICNT0 expires at 56 elements, so onlyeight one-byte elements are included in the fourth stream vector.Streaming engine 125 masks the remaining bytes indicated at 3925 by zerofilling them using the alignment network as described hereinabove.

After ICNT0 expires, the next loop level DIM1 is entered, as indicatedat 3911. In this example, DIM1 specifies a distance of 128 bytes;therefore fetch 5 3926 begins at address 0x128 and the inner loop isrepeated to produce four stream vectors loaded with 56 bytes of elementdata. This repeats seven times since ICNT1=7 in this example.

After ICNT1 expires, the next loop level DIM2 is entered, as indicatedat 3912. In this case, DIM2 specifies a distance of 80 bytes; thereforefetch 29 3927 begins at address 0x080 and the inner loop is repeated toproduce four stream vectors loaded with 56 bytes of element data.Similar to 3925, eight bytes of element data is masked as indicated at3928. This pattern repeats seven times since ICNT1=7 in this example.

TABLE 31 Linear stream example in normal mode ELEM_BYTES 1 byte VECLEN16 elements DIMFMT 3-D START ADDR 0x0 ICNT0 56 ICNT1 7 ICNT2 2 ICNT3 0ICNT4 0 ICNT5 0 DIM1 128 DIM2 80 DIM3 0 DIM4 0 DIM5 0 DECDIM 000DECDIM_WIDTH xxx STREAM VECTOR SIZE 16 bytes

FIG. 40 illustrates an example of a linear stream data strip miningtransfer 4000 in which the DECDIM flags are set to “010b” as shown inTable 30 to associate DECDIM_WIDTH with DIM2. Table 32 lists the streamparameters that are placed in the stream template register 2900 (FIG.29). In this example, VECLEN=16 elements, and each element is one byte.Therefore, each stream vector includes 16 bytes of array elements data.The inner loop is specified by ICNT0=16 bytes, therefore streamingengine 125 will make a fetch to system memory 130 (FIG. 1) to fetch 16bytes of array data in each iteration of the inner loop. In this case,fetch 1 indicated at 4021 actually retrieves 64 bytes of data fromsystem memory 130, but only 16 bytes of data beginning at address 0x0are used to form the first stream vector, in response to ICNT0 asindicated at 4010. The rest of the vector provided to processing unitcore 110 (FIG. 1) is zero filled by alignment network 3820/3821 (FIG.39) as described hereinabove.

Since ICNT0 expires on the first fetch to system memory, the next looplevel DIM1 is entered, as indicated at 4011. In this example, DIM1specifies a distance of 128 bytes; therefore fetch 2 4022 begins ataddress 0x128. ICNT1=7, therefore this loop is repeated seven times,such that fetch 2 4022, up to fetch 7 4023 access system memory 130 toform six additional stream vectors to provide to processing unit core110.

After ICNT1 expires, the next loop level DIM2 is entered, as indicatedat 4012. In this case, DIM2 specifies a distance of 80 bytes; thereforefetch 8 4024 begins at address 0x080 and the inner loop is repeated toproduce a single stream vector loaded with 16 bytes of element data.This loop repeats up to fetch 14 4025, when ICNT 1 expires again and thenext loop level DIM2 is entered again.

After ICNT1 expires again, the next loop level DIM2 is entered, asindicated at 4026. Again, DIM2 specifies a distance of 80 bytes;therefore fetch 15 4026 begins at address 0x160 and the inner loop isrepeated to produce a single stream vector loaded with 16 bytes ofelement data. This loop repeats up to fetch 21 4027, when ICNT 1 expiresagain and the next loop level DIM2 is entered again.

After ICNT1 expires again, the next loop level DIM2 is entered, asindicated at 4026. Again, DIM2 specifies a distance of 80 bytes;therefore fetch 22 4028 begins at address 0x240 and the inner loop isrepeated to produce a single stream vector loaded with 16 bytes ofelement data. However, in this case, the DECDIM_WIDTH parameter 4014 isset to be 248 elements, which is also 248 bytes in this example.Therefore, the array data elements in the border region indicated at4029 are not to be used in the signal processing application that isconsuming this stream. Metadata produced by address generator 2811/2821(FIG. 28) and stored in reference queue 2815/2825 (FIG. 28) is used bycontrol logic 3814 (FIG. 38) to control alignment network 2820/2821(FIG. 38) to mask the data in border region 4029. In this example, thedata in each stream vector that involves border region 4029 is set to avalue of “0” in response to the DECDIM_WIDTH parameter and DECDIM flagsthat were stored in the stream template register 2900 (FIG. 29).

This loop repeats up to fetch 28 4029, when ICNT 1 expires again. Inthis example, ICNT also expires after these four repetitions and thestream is complete.

TABLE 32 Linear stream example, data strip mining, DECDIM on DIM2ELEM_BYTES 1 byte VECLEN 16 elements DIMFMT 3-D START ADDR 0x0 ICNT0 16ICNT1 7 ICNT2 4 ICNT3 0 ICNT4 0 ICNT5 0 DIM1 128 DIM2 80 DIM3 0 DIM4 0DIM5 0 DECDIM 010 DIM2 DECDIM_WIDTH 248 STREAM VECTOR SIZE 16 bytes

FIG. 41 illustrates an example of a linear stream data strip miningtransfer 4100 in which the DECDIM flags are set to “010b” as shown inTable 30 to associate DECDIM_WIDTH with DIM2. Table 33 lists the streamparameters that are placed in the stream template register 2900 (FIG.29). This example is similar to the example of FIG. 40, except thatICNT2 is set to 5, as shown in Table 33. The DIM1 and DIM2 level loopare performed in a similar manner from fetch 1 4121 to fetch 28 4128.Data in border region 4029 is masked in the same manner as described inFIG. 40 in response to DECDIM_WIDTH 4012.

However, in this example, ICNT2=5. Therefore, streaming engine 125prepares to generate addresses for another repetition of the DIM2 loop.However, DECDIM_WIDTH 4112 has now underflowed, indicating that theremaining stream vectors for border region 4130 are to be set to nullvectors. The underflow condition is referred to as being “saturated.” Inthis example, null vectors are set to “0”. When the DECDIM_WIDTH countis saturated, there is no need to access system memory for array elementdata, since the stream vectors are set to null values. Control logicwithin address generator 2811/2821 suppresses address generation inresponse to the DECDIM_WIDTH being saturated so that no accesses aremade to the TLB 2812/2822 (FIG. 28) and no accesses are made to systemmemory 130 (FIG. 1) to produce the null vectors. However, metadata isformed by the control logic 3814 and stored in reference queue2815/2825. Control logic 3814 then uses the metadata to create the nullvectors using alignment network 2820/2821.

In this manner, a stream of array elements is provided to processingunit core 110 that is responsive to the stream parameters, but fetchcycles to system memory and the TLB are avoided for the null vectors.

TABLE 33 Linear stream example, data strip mining, DECDIM on DIM2 withDECDIM_WIDTH saturation ELEM_BYTES 1 byte VECLEN 16 elements DIMFMT 3-DSTART ADDR 0x0 ICNT0 16 ICNT1 7 ICNT2 5 ICNT3 0 ICNT4 0 ICNT5 0 DIM1 128DIM2 80 DIM3 0 DIM4 0 DIM5 0 DECDIM 010 DIM2 DECDIM_WIDTH 248 STREAMVECTOR SIZE 16 bytes

FIG. 42 illustrates an example of a linear stream data strip miningtransfer 4200 in which the DECDIM flags are set to “001b” as shown inTable 30 to associate DECDIM_WIDTH with DIM1. Table 34 lists the streamparameters that are placed in the stream template register 2900 (FIG.29). This example is similar to the example of FIG. 40, except that theDECDIM_WIDTH count is linked to DIM1 instead of DIM2. The DIM1 levelloop is performed in a similar manner from fetch 1 4221 to fetch 3 4222.

At fetch 4 4223, DECDIM_WIDTH count reaches zero and data in borderregion 4224 is masked using alignment network 3820/3821 as described inmore detail hereinabove.

On the next iteration, DECDIM_WIDTH count is saturated and fetches tosystem memory and to the TLB are suppressed as described hereinabove inmore detail. In this manner, stream vectors 4225, 4226, and 4227 areformed by streaming engine 125 without accessing system memory or theTLB.

After ICNT1 expires, the next loop level DIM2 is entered, as indicatedat 4212. In this case, DIM2 specifies a distance of 80 bytes; thereforefetch 8 4228 begins at address 0x080 and the inner loop is repeated toproduce a single stream vector loaded with 16 bytes of element data.This loop repeats up to fetch 11 4029, where a portion of the streamvector is masked in response to DECDIM_WIDTH count 4214 and theremaining three null stream vectors are formed by SE 125 withoutaccessing system memory.

In this example, ICNT2=4, so this same loop of system access andformation of null vectors without system access is repeated two moretimes, as indicated at 4230.

TABLE 34 Linear stream example, DECDIM on DIM1 with DECDIM_WIDTHsaturation ELEM_BYTES 1 byte VECLEN 16 elements DIMFMT 3-D START ADDR0x0 ICNT0 16 ICNT1 7 ICNT2 4 ICNT3 0 ICNT4 0 ICNT5 0 DIM1 128 DIM2 80DIM3 0 DIM4 0 DIM5 0 DECDIM 001 DIM1 DECDIM_WIDTH 392 STREAM VECTOR SIZE16 bytes

FIG. 43 illustrates an example of a linear stream data strip miningtransfer 4300 in which the DECDIM1 flags are set to “001b” as shown inTable 30 to associate DECDIM1_WIDTH with DIM1 and the DECDIM2 flags areset to “010b” as shown in Table 30 to associate DECDIM2_WIDTH with DIM2.Table 35 lists the stream parameters that are placed in the streamtemplate register 2900 (FIG. 29). This example is similar to the examplestream 4000 of FIG. 40, except for the addition of a second set ofDECDIMx flags and DECDIMx_WIDTH parameter.

The DIM1 level loop is performed in a similar manner to stream 4000until DECDIM1_WIDTH 4312 saturates. In this example, ICNT0 4310=16 andICNT1=7. As described hereinabove in more detail, once the DECDIM1 WIDTH4312 count saturates then no further system memory accesses are neededfor that loop. In this case, null stream vectors 4320 and 4321 areformed by streaming engine 125 without accessing system memory 130.

After ICNT1 expires, the next loop level DIM2 is entered, as indicatedat 4311. The DECDIM1_WIDTH counter is reloaded with the count value fromthe stream template register 2900. In this case, DIM2 specifies adistance of 80 bytes; therefore fetch 8 4322 begins at address 0x080 andthe inner loop is repeated to produce a single stream vector loaded with16 bytes of element data. This loop repeats until the DECDIM1_WIDTH 4312count again saturates, then no further system memory accesses are neededfor that loop. In this case, null stream vectors 4323 and 4324 areformed by streaming engine 125 without accessing system memory 130.

In this example, ICNT2=4, so this same loop of system access andformation of null vectors without system access is repeated two moretimes.

However, in this case, the DECDIM2_WIDTH parameter 4313 is set to be 248elements, which is also 248 bytes in this example. Therefore, the arraydata elements in the border region indicated at 4325 are not to be usedin the signal processing application that is consuming this stream.Metadata produced by address generator 2811/2821 (FIG. 28) and stored inreference queue 2815/2825 (FIG. 28) is used by control logic 3814 (FIG.38) to control alignment network 2820/2821 (FIG. 38) to mask the data inborder region 4325. In this example, the data in each stream vector thatinvolves border region 4325 is set to a value of “0” in response to theDECDIM2_WIDTH parameter and DECDIM2 flags that were stored in the streamtemplate register 2900 (FIG. 29).

This loop repeats until the DECDIM1_WIDTH 4312 count again saturates,then no further system memory accesses are needed for that loop. In thiscase, null stream vectors 4326 and 4327 are formed by streaming engine125 without accessing system memory 130.

In this example, ICNT3=2 and DIM3=1500, so this entire sequence isrepeated again beginning at address 0x1500 as indicated at 4341.

TABLE 35 Linear stream example, DECDIM1 on DIM1 and DECDIM2 on DIM2ELEM_BYTES 1 byte VECLEN 16 elements DIMFMT 6-D START ADDR 0x0 ICNT0 16ICNT1 7 ICNT2 4 ICNT3 2 ICNT4 1 ICNT5 1 DIM1 128 DIM2 80 DIM3 1500 DIM40 DIM5 0 DECDIM1 001 DIM1 DECDIM1_WIDTH 640 DECDIM2 010 DIM2DECDIM2_WIDTH 248 STREAM VECTOR SIZE 16 bytes

FIGS. 44A, 44B together illustrate how a partial matrix is augmentedwith null vectors by the streaming engine of FIG. 28 for matrixmultiplication. Table 36 lists the stream parameters that are placed inthe stream template register 2900 (FIG. 29). In this example, VECLEN=16elements, and each element is four bytes (32 bits). Therefore, eachstream vector includes 64 bytes of array elements data to match thewidth of MMA 3640 (FIG. 36). The inner loop specified by ICNT0=16elements (64 bytes), therefore streaming engine 125 will make a fetch tosystem memory 130 (FIG. 1) to fetch 64 bytes of array data in eachiteration of the inner loop.

In this example, a matrix 4400 is located in L2 system memory 130 andhas nineteen columns of 32-bit elements and eighteen rows of 32-bitelements, where each element is indicated by “d” in FIGS. 44A, 44B.Since MMA 3640 of this particular example can only handle a 16×16 arrayof 32-bit elements, matrix 4400 is subdivided into four sub-matrices4401, 4402, 4403, 4404.

Using the stream parameters listed in Table 36, streaming engine 125first fetches sub-array 4401 to provide to MMA 3640. Streaming engine125 then fetches sub-array 4402. Sub-array 4402 includes a border region4405 in which all the data elements provided to MMA 3640 need to be setto zero in order for a matrix multiplication operation to performed byMMA 3640 to operate correctly. As described hereinabove in more detail,streaming engine 125 uses DECDIM1_WIDTH 4410 to define the extent ofmatrix 440, which in this example is nineteen elements.

In this case, the DECDIM1_WIDTH parameter 4410 is set to be nineteenelements, which is 76 bytes in this example. Therefore, the array dataelements in the border region indicated at 4405 are not to be used inthe signal matrix multiplication application that is consuming thisstream. Metadata produced by address generator 2811/2821 (FIG. 28) andstored in reference queue 2815/2825 (FIG. 28) is used by control logic3814 (FIG. 38) to control alignment network 2820/2821 (FIG. 38) to maskthe data in border region 4405. In this example, the data in each streamvector that involves border region 4405 is set to a value of “0” inresponse to the DECDIM1_WIDTH parameter and DECDIM1 flags that werestored in the stream template register 2900 (FIG. 29).

Streaming engine 125 then begins fetching sub-array 4403. At fetch 4412,DECDIM2_WIDTH count reaches zero and is saturated and fetches to systemmemory and to the μTLB are suppressed as described hereinabove in moredetail. In this manner, stream vectors for border region 4406 are formedby streaming engine 125 without accessing system memory or the μTLB.

Streaming engine 125 then begins fetching sub-array 4404. Fetches tosystem memory are performed at 4413 and 4414 and the border region 4405is again masked by alignment network 2820/2821 as described hereinabovein response to DECDEM1_WIDTH saturating. On the next cycle,DECDIM2_WIDTH count reaches zero and is saturated and fetches to systemmemory and to the TLB are suppressed as described hereinabove in moredetail. In this manner, stream vectors for border region 4406 insub-array 4404 are formed by streaming engine 125 without accessingsystem memory or the TLB.

TABLE 36 Linear stream example, DECDIM1 on DIM3 and DECDIM2 on DIM2ELEM_BYTES 4 bytes VECLEN 16 elements DIMFMT 6-D START ADDR 0x0 ICNT0 16ICNT1 16 ICNT2 3 ICNT3 3 ICNT4 3 ICNT5 1 DIM1 32 DIM2 512 DIM3 16 DIM4 0DIM5 0 DECDIM1 011 DIM3 DECDIM1SD off DECDIM1_WIDTH 19 DECDIM2 010 DIM2DECDIM2SD 001 DIM1 DECDIM2_WIDTH 576 STREAM VECTOR SIZE 64 bytesNull Stream Vectors by Count

In the examples described hereinabove, several ways of padding streamvectors with constant values and several ways of forming null streamvectors without accessing system memory were described that are based ona specified value for a DECDIMx_WIDTH count. In another example, it maybe useful to specify a number of null vectors to be inserted in a streamby the streaming engine.

Creation of a Convolution neural network (CNN) Toeplitz style matrix onthe fly requires zero or constant values fed into the MatrixMultiplication Accelerator after the last feature map in the CNN layer.In linear algebra, a Toeplitz matrix or diagonal-constant matrix inwhich each descending diagonal from left to right is constant. Asdescribed with regard to FIG. 36, MMA 3640 has a fixed number of rowswhich need to be filled prior to starting matrix multiplication. Therows remaining during creation of Toeplitz matrix cannot have a junkvalue, otherwise the results will be wrong.

Assuring that all unused data elements are set to zero or to a selectednull value using software requires allocation of memory and execution ofinstructions to write out the null values.

In an example, a loop end zero (LEZR) feature is implemented in thestreaming engine 125 (FIG. 28) hardware. When the streaming enginedimension for the last feature map expires, a number of null rows arefed to the streaming engine without reading data from the memory. Inthis example, streaming engine 125 will send a full 64-byte streamvector on each fetch by the processing unit core 110, thus any dataformatting, scaling, and replay during the normal dimensional loop isnot adhered to. The data is then provided to the matrix multiplicationaccelerator 3640. The rows fed to the matrix accelerator after the CNNnetwork last feature expires makes the matrix complete and ready forblock matrix multiplication. There is not any overhead in softwareneeded and improves performance, helps to reduce software code size andcomplexity.

In this example, an eight-bit LEZR_CNT (LEZR count) field 2933 isprovided in stream template 2900 (FIG. 29). This allows up to 255 nullvectors to be inserted in a stream by streaming engine 125 withoutaccessing system memory. A three-bit LEZR flag 3023 is included in theflag field 2921 of stream template 2900. An example definition of theLEZR flags is included in Table 37.

TABLE 37 LEZR flags to control data strip mining operation LEZR Meaning000b Normal operating mode 001b Start sending null vectors to processingunit core at end of ICNT0 010b Start sending null vectors to processingunit core at end of ICNT1 011b Start sending null vectors to processingunit core at end of ICNT2 100b Start sending null vectors to processingunit core at end of ICNT3 101b Start sending null vectors to processingunit core at end of ICNT4 110b Start sending null vectors to processingunit core at end of ICNT5 111b Reserved

Referring to FIG. 38, control logic 3814 can control each of themultiplexers on alignment networks 3820, 3821 to force a null value ontoselected elements of a stream vector based on the meta-data provided byreference queue 2815. In this manner, an entire stream vector can be setto a null value without fetching any data from system memory. In anexample, the null value is “0.” In another example, a predefined valueor pattern may be used to represent a null value.

In another example, control logic 3814 can control each of themultiplexers on alignment networks 3820, 3821 to force a selected valueonto selected elements of a stream vector based on the meta-dataprovided by reference queue 2815. In this manner, an entire streamvector can be set to a selected value, such as a min value or a maxvalue without fetching any data from system memory.

In this example, control logic in the address generator 2811/2821 (seeFIG. 28) performs count tracking for the six levels of nestediterations. When a loop count for the dimension specified by LEZRexpires, it signals that a null value or a selected value is to beinserted into the vector stream without fetching data from memory forthe null value or selected value vector for a number of stream vectorsspecified by the LEZR field in stream template 2900.

Metadata produced by the address generator is pushed into the streamreference queue 2815/2825 (see FIG. 28). On the backend, when processingunit core 110 (FIG. 1) performs a read, this metadata is popped out andsent to control logic 3814 in alignment network 2820/2821 with the lanesto be nulled or set to a selected value without reading data from systemmemory.

FIG. 45 illustrates adding null vectors to a stream using the LEZRfunction. In this example, multiple feature maps indicated at 4501 arestored in system memory L2 130 (FIG. 1). A stream template is set up bya software application in which ICNT1 defines the number of filter rows(Fr) in a feature map, ICNT2 defines a number of filter columns (Fc) ina feature map, and ICNT3 defines a number (N1) of input feature maps.ICNT0 defines the number of elements of the feature maps 4501 that arefetched by the streaming engine from a row. In this example, foreight-bit elements ICNT0 will be set to 64, and for sixteen-bit elementsit will be set to 32. Streaming engine 125 fetches the feature mapsaccording to the multidimension stream template as described in moredetail above to form stream 4500 as indicated at 4502. Stream 4500 isprovided to MMA 3640 as a B matrix as described in more detailhereinabove.

In this example, the MMA width can be selected to be 16, 32, or 64elements, depending on the size of the elements, as described withrespect to FIG. 36. N1*Fr*Fc forms the rows of the B matrix. This valueis not necessarily a multiple of the selected MMA width. Therefore, anadditional number of null vectors are formed by specifying LEZR_CNT inthe stream template, where LEZR_CNT is defined by expression (4).pad_zero_rows=MMA_width−(N1*Fr*FC%MMA_width)  (4)Pad Value

In some applications, such as a pooling operation in a convolutionneural network for maximum (max), minimum (min), and average pooling,the end of a column of image pixels needs to be either a max or a minvalue. Similarly, analysis tools for various deep learning neuralnetworks, such as TensorFlow, Caffe networks, etc. require arbitraryzero, max, or min padding for the pooling operations.

In this example, a three-bit pad value (PADVAL) flag 3023 is included inthe flag field 2921 of stream template 2900. An example definition ofthe PADVAL flags is included in Table 38. Pad size is done on a fullelement, as defined by the ELTYPE flags 3001 (FIG. 30) in streamtemplate 2900 (FIG. 29). In this example, the default value of zero isselected by setting the PADVAL flag 3023 to 000b, “unsigned min.”

TABLE 38 PADVAL flags to control data strip mining operation PADVALMeaning 000b Unsigned min, default value of zero 001b Unsigned max 010bSigned min 011b Signed max 100b Reserved 101b Reserved 110b Reserved111b Reserved

In an example, a stream vector is formed using the specified pad valueas the last element of a stream vector of the stream. In anotherexample, another flag field (such as LEZR flags 3023, Table 37) may beused to specify a selected dimension on which to include a pad value.

Referring to FIG. 38, control logic 3814 can control each of themultiplexers on alignment networks 3820, 3821 to force a null value ontoselected elements of a stream vector based on the meta-data provided byreference queue 2815. In this manner, an entire stream vector can be setto a specified null value without fetching any data from system memory.In an example, the null value an unsigned max value. In another example,other predefined values or patterns may be used to represent a nullvalue.

In an example, control logic 3814 can control each of the multiplexerson alignment networks 3820, 3821 to force a selected value onto selectedelements of a stream vector based on the meta-data provided by referencequeue 2815. In this manner, an entire stream vector can be set to aselected value, such as a min value or a max value without fetching anydata from system memory.

In this example, control logic in the address generator 2811/2821 (seeFIG. 28) performs count tracking for the six levels of nestediterations. When a loop count for the end of a stream expires, itsignals that a null value or a selected value is to be inserted into thevector stream without fetching data from memory for the null value orselected value vector, as defined by the PADVAL flags 3024 in streamtemplate 2900.

Metadata produced by the address generator is pushed into the streamreference queue 2815/2825 (see FIG. 28). On the backend, when processingunit core 110 (FIG. 1) performs a read, this metadata is popped out andsent to control logic 3814 in alignment network 2820/2821 with the lanesto be nulled or set to a selected value without reading data from systemmemory.

In order to achieve this in software code requires performing a permuteoperation. In an example simulation, performance of the hardware basedPADVAL solution was 4× better than the software solution for imagewidth>64 and 2× better performance for an image with <64; furthermore,the software solution required three different loops.

FIG. 46 illustrates formation of a stream by inserting null orpredefined data vectors by a streaming engine, such as streaming engine125 of FIG. 28. In this example, at 4600 a stream is opened on astreaming engine by storing stream parameters in a stream templateregister (2900, FIG. 29) within the streaming engine. The streamparameters include an element size of the array, a number of elements toinclude in each vector of a stream, a number of vectors to include inthe stream for each dimension of the array, and a width indicator for aselected dimension of the array, such as a DECDIM flag and aDECDIM_COUNT, see Table 30.

At 4601, an address stream is generated according to the streamparameters stored in the stream template. Metadata is saved thatindicates loop counts, end of loop, remaining width count, etc.

At 4602 a line of matrix data is fetched by the streaming engine fromsystem memory using the sequence of addresses generated by the addressgenerator.

At 4603, a check is made to see if a width count parameter is associatedwith the current dimension of the multi-dimension stream. If not, anormal stream vector is formed at 4605.

If a width count parameter is associated with the current dimension,then at 4604, a check is made to determine if the width count isdepleted. If not, a normal stream vector is formed at 4605.

If the width count is depleted, then at 4606 a check is made todetermine the width count is saturated. If not, then a stream vector isformed at 4607 by masking a portion of the vector that exceeds the widthcount. In some examples, the mask may insert a value of zero. In anotherexample, a predefined value may be inserted by the mask, such as a minvalue, a max value, etc.

If the width count is saturated, then at 4608 a null vector is formedwithout accessing system memory. In an example, the null vector may beset to all zeros. In another example, the null vector may be set to apredetermined pad value, such as a min value, a max value, etc. Apredetermined pad value may be designated by a flag field, such a PADVALflag 3023 (FIG. 30) in the stream template.

At 4609, if the current dimension is not complete the loop repeats at4602. If the current dimension is complete, then the width count isdecremented at 4610 if it is associated with the current dimension.Otherwise, the width count is not decremented.

At 4611 a check is made to determine if the stream is complete. If not,the process repeats to access more matrix data from the system and toform stream vectors.

At 4612, once the entire matrix has been accessed from memory, the datastream is closed.

FIG. 47 illustrates formation of a stream by inserting null orpredefined data vectors by a streaming engine, such as streaming engine125 of FIG. 28. In this example, at 4700 a stream is opened on astreaming engine by storing stream parameters in a stream templateregister (2900, FIG. 29) within the streaming engine. The streamparameters include an element size of the array, a number of elements toinclude in each vector of a stream, a number of vectors to include inthe stream for each dimension of the array, and a loop end count, suchas loop end zero count 2933 (FIG. 29), and a flag to associate the loopend zero count with a selected dimension of the multidimensional loop,as described in Table 37.

At 4701, an address stream is generated according to the streamparameters stored in the stream template. Metadata is saved thatindicates loop counts, end of loop, remaining width count, etc.

At 4702 a line of matrix data is fetched by the streaming engine fromsystem memory using the sequence of addresses generated by the addressgenerator.

At 4703 a normal stream vector is formed using the data elements fetchedfrom system memory.

At 4704, if the current dimension is not complete the loop repeats at4602. If the current dimension is complete.

At 4705, a check is made to determine if the null count applies to thecurrent dimension. If so, a number n of null vectors equal to the nullcount value in the stream template are formed by the streaming enginewithout accessing null data from system memory. In this example, thedata in the null vectors are set to zero. In another example, apreselected null value may be used to form the null vector, such as amin value, a max value, etc.

At 4707, a check is made to determine if the stream is complete. If not,the process repeats with the next loop at 4708 to access more matrixdata from the system and to form stream vectors.

At 4709, once the entire matrix has been accessed from memory and thespecified null vectors formed without accessing data from system memory,the data stream is closed.

FIG. 48 illustrates an example multiprocessor system. In this example,SoC 4800 includes processor 100 (FIG. 1) (referred to as “processor A”)and it is combined with a second processor 4811 (referred to as“processor B”). Each processor is coupled to a block of shared levelthree (L3) memory 4850 via bus 4851. Processor B includes a block ofunshared level two memory 4812. A direct memory access (DMA) engine 4860may be programmed to transfer blocks of data/instructions from L3 memoryto L2 memory 130 or L2 memory 4812 using known or later developed DMAtechniques. Various types of peripherals 4862 are also coupled to memorybus 4851, such as wireless and/or wired communication controllers, etc.

In this example, processor A, processor B, L3 memory 4850 are allincluded in a SoC 4800 that may be encapsulated to form a package thatmay be mounted on a substrate such as a printed circuit board (PCB)using known or later developed packaging techniques. For example, SoC4800 may be encapsulated in a ball grid array (BGA) package. In thisexample, external memory interface (EMI) 4852 allows additional externalbulk memory 4854 to be accessed by processor A and/or processor B.

In this example, processor B is an ARM® processor that may be used forscalar processing and control functions. In other examples, varioustypes of known or later developed processors may be combined with DSP100. While two processors are illustrated in this example, in anotherexample, multiple copies of DSP 100 and/or multiple copies of processorB may be included within an SoC and make use of the techniques forforming masked and null vectors without accessing system memory providedby streaming engine 125 that are described herein in more detail.

OTHER EXAMPLES

In a described example, a streaming engine includes two closely coupledstreaming engines that can manage two data streams simultaneously. Inanother example, the streaming engine maybe capable of managing only asingle stream, while in other examples the streaming engine is capableof handling more than two streams. In each case, for each stream, thestreaming engine includes an address generation stage, a data formattingstage, and some storage for formatted data waiting for consumption bythe processor.

In a described example, addresses are derived from algorithms that caninvolve multi-dimensional loops, each dimension maintaining an iterationcount. In one example, the streaming engine supports six levels ofnested iteration. In other examples, more or fewer levels of iterationare supported.

In a described example, one-dimensional zero padding of stream vectorsis provided. In another example, two-dimensional zero padding of streamvectors is provided. In yet another example, more than two dimensions ofzero padding may be provided.

In described examples, a complex DSP processor with multiple functionunits and dual data paths is described. In another example, a simplerDSP that is coupled to a stream processor may be used. In anotherexample, other types of known or later developed processors may becoupled to a stream processor, such as a reduced instruction setcomputer (RISC), a traditional microprocessor, etc.

In a described example, the MMA supports 32×32 16-bit matrixmultiplication, and 64×64 8-bit matrix multiplication, and the streamingengine is configured to provide 64-byte stream vectors. In anotherexample, the MMA may be configured to support large or smaller matrixsizes. An associated streaming engine may be configured to providestream vectors that have a size that is larger or smaller than 64 bytes.

In described examples, a processor that consumes a stream of data and astreaming engine that retrieves the stream of data from system memoryare all included within a single integrated circuit (IC) as a system ona chip. In another example, the processor that consumes the stream ofdata may be packaged in a first IC and the streaming engine may bepackaged in a second separate IC that is coupled to the first IC by aknown or later developed communication channel or bus.

In this description, the term “couple” and derivatives thereof mean anindirect, direct, optical, and/or wireless electrical connection. Thus,if a first device couples to a second device, that connection may bethrough a direct electrical connection, through an indirect electricalconnection via other devices and connections, through an opticalelectrical connection, and/or through a wireless electrical connection.

Modifications are possible in the described examples, and other examplesare possible, within the scope of the claims.

The invention claimed is:
 1. A method of operating a streaming engine ina computer system, the method comprising: receiving stream parametersinto control logic of the streaming engine that define amultidimensional array, wherein the stream parameters define a size foreach dimension of the multidimensional array, a first specified widthfor a first selected dimension of the multidimensional array, and asecond specified width for a second selected dimension of themultidimensional array; generating a set of memory addresses associatedwith the multidimensional array based on the stream parameters, whereinthe generating of the set of memory addresses includes determining, foreach address of the set of memory addresses, whether a fetch of therespective address exceeds either the first specified width or thesecond specified width; based on a fetch of a first memory address notexceeding either of the first specified width or the second specifiedwidth, fetching data from a memory coupled to the streaming engineresponsive to the stream parameters using the first memory address;based on a fetch of a second memory address exceeding either the firstspecified width or the second specified width, generating a null elementwithout accessing the memory; and forming a stream of vectors for themultidimensional array responsive to the stream parameters that includesthe data fetched from memory and the null element.
 2. The method ofclaim 1, wherein the generating of the null element is performed withoutaccessing an address lookaside buffer.
 3. The method of claim 1, inwhich the stream parameters include an element size of themultidimensional array, a number of elements to include in each vectorof a stream, and a number of vectors to include in the stream for eachdimension of the multidimensional array.
 4. The method of claim 1, inwhich the null element is set to a value of zero.
 5. The method of claim1, in which a null value for the null element is specified by the streamparameters.
 6. The method of claim 1, wherein the stream parametersdefine the size for each dimension by specifying a loop count for therespective dimension.
 7. The method of claim 1, wherein: the firstspecified width for the first selected dimension is independent of thesize of the multidimensional array in the first selected dimension; andthe second specified width for the second selected dimension isindependent of the size of the multidimensional array in the secondselected dimension.
 8. The method of claim 1, wherein the stream ofvectors includes a first vector that includes the data fetched from thememory and the null element.
 9. The method of claim 1, wherein thestream of vectors includes a first vector that includes the data fetchedfrom the memory and a second vector that is a null stream vector.
 10. Asystem comprising: a system memory; and a streaming engine coupled tothe system memory, wherein the streaming engine comprises: a streamtemplate register to hold stream parameters, wherein the streamparameters define a size for each dimension of a multidimensional array,a first specified width for a first selected dimension of themultidimensional array, and a second specified width for a secondselected dimension of the multidimensional array; address generationlogic coupled to the stream template register and configured to generatea set of addresses based on the stream parameters; a register file withinputs coupled to receive a vector fetched from the system memory usingthe set of addresses; an alignment network with inputs coupled tooutputs of the register file, the alignment network having outputscoupled to outputs of the streaming engine to provide a stream vectorresponsive to the stream parameters; and control logic coupled tocontrol the alignment network and configured to: based on a fetch of afirst address not exceeding either of the first specified width or thesecond specified width, cause the alignment network to provide a dataelement of the vector fetched from the system memory as a first elementof the stream vector; and based on a fetch of a second address exceedingeither the first specified width or the second specified width, causethe alignment network to provide a null element as a second element ofthe stream vector without an access of the system memory.
 11. The systemof claim 10, further comprising a translation lookaside buffer coupledto the address generation logic, wherein the control logic is configuredto, based on the fetch of the second address exceeding either the firstspecified width or the second specified width, cause the alignmentnetwork to provide the null element as the second element of the streamvector without an access of the translation lookaside buffer.
 12. Thesystem of claim 10, in which the null element has a value of zero. 13.The system of claim 10 in which a null value for the null element isspecified by the stream parameters.
 14. The system of claim 10 being asystem on a chip (SoC), further comprising a processing unit coupled tothe outputs of the streaming engine to receive the stream vector. 15.The system of claim 10, wherein: the alignment network includes a set ofmultiplexers coupled to the register file and to the control logic; andeach of the set of multiplexer is configured to provide the null elementas a respective element of the stream vector in response to the controllogic.
 16. The system of claim 10, wherein the stream parameters definethe size for each dimension by specifying a loop count for therespective dimension.
 17. The system of claim 10, wherein: the firstspecified width for the first selected dimension is independent of thesize of the multidimensional array in the first selected dimension; andthe second specified width for the second selected dimension isindependent of the size of the multidimensional array in the secondselected dimension.
 18. A system comprising: a system memory; astreaming engine coupled to access the system memory to form a stream ofstream vectors for a multidimensional array, wherein the streamingengine is configured to: insert a null element into a selected streamvector of either of two dimensions of the multidimensional array withoutaccessing the system memory based on a determination that a memoryaccess exceeds a specified width of either of the two dimensions of themultidimensional array by: generating a set of addresses associated withthe stream of stream vectors; based on a first access associated with afirst address not exceeding the specified width of either of the twodimensions of the multidimensional array: fetching a data element fromthe system memory; and providing the data element in the stream ofstream vectors; and based on a second access associated with a secondaddress that is associated with the selected stream vector exceeding thespecified width of either of the two dimensions of the multidimensionalarray, provide the null element in the selected stream vector withoutaccessing the system memory; and a processing unit coupled to outputs ofthe streaming engine to receive the stream of stream vectors.
 19. Thesystem of claim 18, in which the streaming engine comprises: a streamtemplate register to hold stream parameters, wherein the streamparameters define a size for each dimension of the multidimensionalarray, a first specified width for a first selected dimension of themultidimensional array, and a second specified width for a secondselected dimension of the multidimensional array; and control logiccoupled to receive the stream parameters from the stream templateregister being configured to provide the null element in the selectedstream vector based on the determination that the memory access exceedsthe specified width of either of the two dimensions of themultidimensional array.
 20. The system of claim 19, wherein the streamparameters specify a value for the null element.